Process to obtain an iron / carbon-enriched fraction from the growth of carbon nanofibers in mining tailings

Abstract

2020205337 17 Jul 2020 OF CARBON NANOFIBERS IN MINING TAILINGS nanofibers. The obtained materials have a carbon content between 40-67%. 1 / 7 Figure 1 Figure 2 R e la ti v e i n te n s it y / u .a . 20 20 20 53 37 1 7 Ju l 2 02 0Jul 2020 L 2020205337 17 HV CENTRO UFMG CENTRO UFMG HV WD HFW HV Sig WD Spot HFW10.0 KV 30000x SE 11.0mm 3.0 CENTRO DE MICROSCOPIA UFMG 10.0 kV 100000x SE CENTRO DE MICROSCOPIA UFMG S = SiO (PDF 46-1045) H = Fe2O3 (PDF 24-72) G = FeOOH (PDF 29-713) C = Grafite (PDF 1-646) -Fe = Fe° (PDF 6-696) -Fe = Fe(C) (PDF 31-619) HG G S L01 G S SG H H G HG H G H H H G G G G Inter Relative intensity / u.a. 02 S H S GGS G G S S G SG C a-Fe y-Fe LCVD 900 -Fe C C a-Fe8 10 20 30 40 50 60 70 20 / °

Description

PROCESS TO OBTAIN AN IRON / CARBON-ENRICHED FRACTION FROM THE GROWTH OF CARBON NANOFIBERS IN MINING TAILINGS CROSS REFERENCE

[001] The present application claims priority to Brazilian Patent Application No. BR 10 2019 014935 3, filed on 19 July 2019, the entire contents of which is incorporated herein by reference in its entirety. FIELD OF THE INVENTION [001a] This invention refers to a process of growing carbon nanofibers on iron mining tailings that can be separated into an iron / carbon-enriched fraction and a silica-enriched fraction. The process comprises a carbon reduction and deposition step consisting of heat treatment of the tailings in an atmosphere containing any source of volatile carbon, a step of dispersion / agitation of reduced tailings and a magnetic separation step, thus obtaining materials with high added value after the formation of carbon nanofibers. BACKGROUND OF THE INVENTION

[002] Brazil has the second largest iron ore reserve in the world, estimated at 23 billion tons, and is the third largest producer, after China and Australia. In Brazil, the main ore producing states are Minas Gerais (Iron Quadrangle) and Para (Serra dos Carajas), which account for more than 95% of Brazilian production. Considering the total iron content, the Brazilian is even more prominent, because the ore from the states of Para and Minas Gerais can reach up to 60% iron content.

[003] Located in the center-south portion of the state of Minas Gerais, the Iron Quadrangle is a region of great economic and environmental importance, as the largest Brazilian producer of iron ore. Due to the characteristics of ore exploited in this location, an increasing generation of tailings can be observed resulting from the type of beneficiation used.

[004] The iron ore currently exploited in the Iron Quadrangle is composed of friable itabirite and / or compact itabirite. Such ore requires comminution and concentration processes in order to release the gangue elements and obtain appropriate concentrations of the iron minerals. The products of the itabirite iron ore beneficiation consist basically of ore with particles smaller than 0.15 mm (pellet feed) and particles with sizes between 0.15 and 6.3mm (sinter feed), in addition to the process tailings.

[005] One of the main environmental concerns related to the extraction of iron is the management of large quantities of tailings generated in the ore beneficiation process, which are mostly disposed of as tailings dams. The beneficiation of 1 ton of ore is estimated to generate approximately 0.4 tons of tailings.

[006] Tailings dams receive and store a pulp with high concentration of water, reagents and solid particles to prevent downstream pollution and store water for recirculation at the beneficiation plant. However, these dams use a large area and cause different environmental impacts, in addition to presenting a catastrophe risk, including their collapse. Recent dam collapse events in Brazil exemplify the inherent risk of these structures.

[007] The iron ore beneficiation tailings are basically composed of goethite (FeOOH), hematite (Fe;03), quartz (SiOz), kaolinite {Al2Si20s(OH)a}). According to ABNT Standards 10004-10007, these tailings are classified as class Ill (inert).

[008] Typically, the concern with the reuse of waste is relatively recent in Brazil and has become the subject of research aimed at reducing the negative environmental impacts associated with waste. In Brazil, concerns focused on the considerable volume of waste generated in the mining industry stand out. More specifically, regarding tailings from iron ore benficiation, its reuse and addition of value have been largely addressed. For example, studies for applications in civil construction industry, such as concrete interlocked paving block production and improvement of granular soil resistance. Usually described as a material with granulometric characteristics of silt and clay, iron ore tailings prove to be a suitable component for filling voids in concrete, improving compressive and tensile strength, and having potential for use as an addition to the concrete batch composition and also as a partial replacement for the natural aggregate.

[009] The tailings have also been used for producing high-strength ceramic tiles, removing cationic and anionic dyes, synthesizing MCM-41 (mesoporous molecular material), synthesizing magnetic graphene, coating mortar, Fenton process to degrade dyes, porous geopolymer to remove Cu (Il) from wastewater, and other processes.

[0010] In recent years, reinforcements consisting of carbon nanostructures such as carbon nanotubes, fullerenes, graphene and carbon nanofibers have been researched due to their increased mechanical, electrical and thermal properties.

[0011] Carbon nanotubes are composed of graphite sheets rolled up and parallel to the axis of the tubes, with the basal planes on the surface showing little reaction. Carbon nanofibers consist of graphite plates stacked along the fiber axis in a cone shape, presenting the prismatic plans exposed and quite reactive. One of the main characteristics of these structures is the presence of a large number of extremities that favor physical or chemical interactions, especially adsorption.

[0012] Since carbon nanofibers consist of a continuous reinforcement (or blanket- shaped) of a high specific surface area, associated with the fact that they can be obtained at low cost and in large quantities, carbon nanofibers have proven advantageous compared to traditional carbon nanotubes, being investigated for different technological applications, e.g. polymer reinforcement, adsorbents, catalysts and even as reinforcing agents for the production of ore pellets.

[0013] These materials can be produced in different ways, including arc discharge, laser vaporization and catalytic decomposition. Among these methods, the catalytic is the simplest, the cheapest and the one that produces the least amount of amorphous carbon alongside the nanotubes, thus not requiring further purification. This method consists of the catalytic decomposition (Fe, Ni and Co) of some hydrocarbons at temperatures ranging from 400 to 1200 °C. The catalytic method can be used in the production of both nanofibers and carbon nanotubes.

[0014] The prior art includes publications related to processes of growing nanofibers and carbon nanotubes as exemplified below.

[0015] The publication of KUMAR et al. (2010), KUMAR, M., ANDO, Y. Chemical Vapor Deposition of Carbon Nanotubes: A Review on Growth Mechanism and Mass Production. Journal of Nanoscience and Nanotechnology. Vol. 10, 3739-3758, 2010, presents the chemical vapor deposition process (CVD). This publication describes the progress of the prior art and an overview of the process.

[0016] Although KUMAR et al. (2010) discusses the growth of nanotubes, the concept is equivalent for nanofibers. The main catalysts commonly employed are also discussed, as well as the supporting materials (substrate). The process involves a hydrocarbon vapor going (usually for 15 to 60 minutes) through a tubular reactor in which a catalyst material is present at a sufficiently high temperature, preferably 600 to 1200°C, to decompose the hydrocarbon. The most commonly used metals are Fe, Co, Ni, due to two main reasons: (i) high solubility of carbon in these metals at high temperatures; and (ii) high rate of carbon diffusion in these metals. The substrates commonly used in CVD include graphite, quartz, silicon, silicon carbide, silica, alumina, aluminum-silicate (zeolite), CaCO3, magnesium oxide, among others.

[0017] The Brazilian patent application PI 1104699-6, entitled "Modified vermiculite from carbon nanostructure deposition”, filed on August 31, 2011 on behalf of the Federal University of Minas Gerais, discloses the production of nanostructured composites with magnetic cores and amphiphilic properties based on vermiculite partially coated with carbon nanostructures, for industrial process applications as catalytic support, adsorbent, in the removal of oily contaminants, and breaking and formation of emulsions. This coating can be made from a gaseous carbon source or a solid source impregnated on the surface of vermiculite. Modified vermiculite can be applied in various sectors, such as the fuel and oleochemical industries, treatment of effluents, food, pharmaceutical, chemical, and other.

[0018] The Brazilian patent application PI 1004737-9, entitled "Process of conversion of red slurry tailings into amphiphilic materials and their applications in the formation and recovery of emulsifying material", filed on October 18, 2010 on behalf of the Federal University of Minas Gerais, discloses the use of carbon-coated particles obtained by the process of conversion of red slurry tailings, from nano to micrometer dimensions, in the breaking and formation of emulsions, in order to give a correct destination and also add value to the residue. The production process of the amphiphilic particles involves a single step with reduction of the iron oxides / hydroxides found in the red slurry to form magnetic cores and deposition of carbon from different types of organic compounds, used as carbon source.

[0019] The process for producing these particles in PI 1004737-9 can be described as: (i) heating of the red slurry in a furnace at temperatures between 300 - 1000°C; (ii) introducing controlled amounts of an carbon source organic compound, e.g. methane, ethane, ethylene, propane, propene, butane, butene, pentane, hexane, hexene, benzene, toluene, xylene, etc., which comes into contact with the iron-rich material, in nitrogen atmosphere or not; (iii) iron hydroxides reduction by the organic compound to form the magnetic phases (metallic iron and / or magnetite); and (iv) deposition of carbon in the form of amorphous carbon, graphite, nanofibers and nanotubes.

[0020] The Brazilian patent application PI 1104701-1, entitled "Amphiphilic composites for application in industrial processes," filed on August 31, 2011 on behalf of the Federal University of Minas Gerais and of the Centro de Desenvolvimento da Tecnologia Nuclear - CDTN, discloses a process for the production of amphiphilic magnetic particles based on chrysotile partially coated with carbon nanostructures and magnetic cores for industrial process applications including catalytic support, adsorbent or in the breaking and formation of emulsions. Chrysotile can be impregnated with different catalyst metals to obtain magnetic composites. The partial coating of carbon, in the form of amorphous carbon, graphite, nanofibers or nanotubes, is made through a process, in a single step, involving the reduction of the metallic catalysts to form the magnetic core. These catalyst metals are selected from the group comprising Fe, Co, Ni, Ru, Rh, Pd or Pt salts, or metal alloys. For the partial deposition of carbon different types of organic compounds such as methane, ethane, propane, etc., can be used.

[0021] Prior art references generally refer to obtaining nanoparticles by the chemical vapor deposition technique. Additionally, no previous studies related to nanoparticle growth using iron ore processing tailings, but bauxite processing tailings (red slurry) and other silicate sources have been observed.

[0022] Although many works seek the reuse of iron mining tailings, as discussed above, the vast majority leads to products with relatively low added value, as bricks, paving base, cement and concrete components. This invention aims to transform tailings into high value-added products with scale processing compatible to their generation.

[0023] Thus, in this invention, the iron found in tailings is used as a catalyst to grow carbon nanofibers. Encapsulated reduced iron carbon nanofibers can be separated from silica by mechanical, magnetic separation or flotation processes. Metallic iron or carbide is formed inside the fibers, which can be applied directly in steelmaking processes. OBJECTS OF THE INVENTION

[0024] This invention aims to provide a process for growing carbon nanofibers on iron mining tailings and the subsequent obtention of an iron / carbon-enriched fraction and another fraction enriched with silica and other chemical elements.

[0025] This invention also aims to provide a process for obtaining a product with high added value after the formation of carbon nanofibers and concentration by magnetic separation.

[0026] Another objective of this invention is providing a process applied to iron mining tailings to obtain products with high added value, allowing a reduction of tailings disposal in dams. SUMMARY OF THE INVENTION

[0027] The preferred embodiment of this invention discloses a process for growing carbon nanofibers in iron mining tailings and obtaining an iron / carbon-enriched fraction comprising the following steps: a) heat treating the iron ore beneficiation tailings at a temperature of 500 to 1200 °C at an atmosphere containing any volatile carbon source, which may or may not be followed by H», for 30 minutes to 6 hours; b) dispersing the treated tailings and perform mechanical shaking of the treated tailings for 1 to 60 minutes; c) magnetic separation by bringing a magnet close to the outer surface of the vessel containing the dispersion of the material in water, for 1 to 30 minutes; d) separating the magnetic fraction, rich in iron and carbon, from the non- magnetic fraction, rich in silica and other chemical elements; and e) drying the two fractions obtained. BRIEF DESCRIPTION OF FIGURES

[0028] This invention is detailed based on the corresponding figures.

[0029] Figure 1 shows scanning microscope images of sample tailings before and after the CVD process.

[0030] Figure 2 shows X-ray diffraction (XRD) of ultra-fine tailings after heat treatment at 900 °C and after the CVD process.

[0031] Figure 3 shows Mossbauer spectra obtained at room temperature for ultra-fine tailings samples before and after CVD, LO1 and LO1CVD900.

[0032] Figure 4 shows thermogravimetry curves obtained in atmosphere air for the samples LO1 and LO1CVD900.

[0033] Figure 5 shows X-ray diffraction of the sandy tailings samples after heat treatment at 900 °C and after the CVD process.

[0034] Figure 6 shows the Méssbauer spectra obtained at room temperature for sandy tailings samples before and after CVD, A01 and AG1CVD900.

[0035] Figure 7 shows thermogravimetric curves obtained at atmosphere air for samples AO1 and AO1CVD900.

[0036] Figure 8 shows scanning electron microscope (SEM) images for samples AO1, A01CVDI00 without grinding and their magnetic fractions and AO1CVD900_Si (white particles).

[0037] Figure 9 shows thermogravimetry curves for the AO1CVDS00 samples without grinding and their magnetic and non-magnetic fractions. DETAILED DESCRIPTION OF THE INVENTION

[0038] Although this invention may be susceptible to different modalities, preferred embodiments are shown in the following drawings and detailed discussion with the understanding that this description should be considered an example of the principles of the invention and is not intended to limit this invention to what is shown and described here.

[0039] The main approach of this invention is related to a process of growing carbon nanofibers in mining tailings and the subsequent obtention of an iron / carbon-enriched fraction and another fraction enriched with silica and other chemical compounds. More specifically, this invention refers to a process of obtaining materials with high added value after the formation of carbon nanofibers and a possible magnetic separation comprising the following steps: a) heat treating the iron ore processing tailings at a temperature of 500 to 1200 °C at an atmosphere containing any volatile carbon source, which may or may not be followed by H,, at a flow rate between 10-400 mL / min, preferably 200 mL / min, for 30 minutes to 6 hours, preferably 1 hour; b) dispersing the treated tailings and performing mechanical shaking of the treated tailings for 1 to 60 minutes, preferably 40 minutes; c) performing the magnetic separation by bringing a magnet to the outer surface of the vessel containing the material dispersed in water, for 1 to 30 minutes, preferably 15 minutes; d) separating the magnetic fraction, rich in iron and carbon, from the non- magnetic fraction, rich in silica and other chemical compounds; and e) drying the two fractions obtained.

[0040] The volatile carbon source in step a) is selected from the group comprising methane, ethane, ethylene, propane, propene, butane, butene, pentane, pentene, hexane, hexene, benzene, toluene, xylene, naphthalene, decalin, methanol, ethanol, propanol, butanol, acetaldehyde, formaldehyde, propanal, butanedial, methyl acetate, ethyl acetate, ethyl propanoate, isopropyl propanoate, butyl ethanoate, methyl-propyl ketone, propanone, pentanone, hexanone, acetonitrile.

[0041] The dispersion of the materials referred to in step b) can be either dry or wet. In the case of the wet dispersion, solvents selected from the group comprising water, ethanol, acetone, hexane, acetonitrile, methanol, propanol, butanol, isopropyl alcohol, ethyl acetate, chloroform, and other, are used.

[0042] The mechanical / magnetic separation of the carbon nanofibers from the silica can be performed by two processes: with mechanical shaking or using of ultrasound, in addition to a combination of both. Initially, the material is crushed to reduce the particle size to 10-30um. This crushed solid is then transferred to a vessel with water and the mixture is submitted to ultrasound, for disintegration of the particles, for a period of approximately 15 minutes.

[0043] The magnet referred to in step c) is selected from the group comprising iron magnet, neodymium magnet, cobalt samarium magnet, alnico magnet, rare-earth magnet.

[0044] The magnetic separation referred to in step d) can be performed in a high- gradient drum or carousel magnetic separator, either wet or dry, being not limited to these.

[0045] Mining tailings consist of a mixture of iron oxides, silicon and aluminum and others, and come from the separation and flotation processing. Although often referred to as tailings, these materials still have a relatively high iron content (10-60%) but have physicochemical characteristics (such as low grain size, colloid formation, etc.) that make it difficult or even prevent processing them in a technically and / or economically feasible manner.

[0046] Iron ore beneficiation tailings are selected from the group containing iron ore content greater than 5%, comprising ultra-fine iron mining tailings, sandy tailings, laterite, gangue, mining waste, among others.

[0047] The studies involved in this invention used ultra-fine tailings, also called slurry, from the desliming stage, and sandy tailings, from the concentration stage (flotation and / or magnetic concentration), both from the iron ore beneficiation. The specifications of materials produced after chemical vapor deposition (CVD) using ultra-fine tailings and sandy tailings as a catalyst, have indicated that 900 °C is the best temperature for growth of carbon nanostructures using methane as a carbon source. At this temperature more carbon nanostructures are formed with higher quality.

[0048] The material obtained have a carbon content between 40-67%. Carbon nanofibers can be separated from the silica matrix containing other chemical compounds by various processes, but the most efficient proved to be the magnetic separation process.

[0049] Examples of the results obtained for each material are detailed below. EXAMPLES

[0050] Experimental tests were carried out using the two types of tailings separately, the ultra-fine tailings and sandy tailings from iron mining. The iron ore tailings were supplied by Vale.

[0051] The tailings samples, both ultra-fine and sandy, were previously dried in a kiln for 24 hours at 80 °C and then undergone a chemical vapor deposition (CVD) process.

[0052] The CVD was performed in a horizontal tubular furnace at 700, 800 or 900 °C (at heating rate of 10 °C / min) and a reaction time between 30 and 360 minutes under a CHa atmosphere.

[0053] These samples were named according to the type of tailings (ultra-fine or sandy tailings), batch and temperature used in the CVD process. For example, LO1CVD900 refers to the ultra-fine tailings sample from batch 01 that undergone a CVD process at 900 °C.

[0054] Then, the material obtained was dispersed in water and placed in the ultrasound for 30 minutes. The next step, magnetic separation, was performed with a magnet to separate the magnetic fraction rich in iron and carbon from a second fraction rich in silica and other chemical compounds.

[0055] The ultra-fine and sandy tailings and the fractions obtained with the process described above were characterized by X-ray diffraction (XRD), X-ray fluorescence, Méssbauer spectroscopy, Raman spectroscopy, thermogravimetry and atomic absorption.

[0056] The results showed that the tailings consist mostly of iron oxides such as hematite (Fe20s) and goethite (FeOOH), silicon (SiOz), with low amounts of aluminum oxide (Al,03), manganese (Mn), titanium oxide (TiOz), calcium oxide (CaO), magnesium oxide (MgO), phosphorus (P). After the heating of the tailings under the carbon source atmosphere, the transformation of the hematite and goethite phases into a-Fe and y-Fe and the production of carbon nanofibers are observed. The magnetic separation was performed to generate the magnetic and non-magnetic fractions: one enriched with iron and one enriched with silica and other chemical compounds. Example 1 — Ultra-fine Tailings

[0057] The ultra-fine tailings sample was previously dried in a kiln for 24 hours at 80°C and, subsequently, 500mg of the dry tailings were added in a quartz tube provided with porous plate in the center capable of supporting the catalyst. The CVD process was performed in two steps: (i) pre-reduction of the material for 30 minutes with a mixture of Nz and Hz in the proportion 1:1 {flow rate of 300 mL min-1 for each gas) at a fixed temperature of 800 °C; and (ii) growth of carbon nano-structures using ethylene and methane as carbon source. For ethylene, the step (ii) was performed at 700 °C for 30 minutes, and for methane the temperatures of 800 and 900 °C for 3 hours are used.

[0058] According to the X-ray diffraction (XRD) and Méssbauer analysis, shown by Figures 2 and 3, it can be seen that the sample LO1 is composed of goethite, hematite and silicon oxide, and after heating the material up to 900 °C the goethite phase is transformed into hematite, and the crystallinity of the hematite phase increases. The sample LO1CVDI00 presents typical carbon nanostructure peaks, in addition to metallic iron. The absence of typical iron oxide peaks after the CVD process indicates that the carbon structures are covering these phases.

[0059] The carbon structures, formed in the CVD process, are evaluated by Raman microscope, as shown in Figure 3. Typical crystalline structure and amorphous bands are observed, with crystalline structures seeming to be in greater proportion.

[0060] Figure 4 shows the TG (thermogravimetry) curves obtained at atmosphere air for samples LO1 and LO1CVDI00, i.e. ultra-fine tailings sample and ultra-fine tailings sample that undergone the CVD process at 900 °C. For the LO1 sample two losses of mass are noted, the first close to 350 °C and the second at 500 °C. These losses of mass must be essentially associated with the loss of water molecules. Each loss is related to a type of water contained in the tailings structure. Probably the first loss is associated with hydration water molecules, whereas the second loss is associated with water molecules that are formed by the dehydroxylation of structure of the material. For material LO1CVDI00 a mass gain event at 500 °C was observed, which should be associated with the oxidation of Fe®, and a mass loss event in the range 550 - 700 °C, characteristic of organized carbon oxidation. Also according to thermal analysis, the carbon content in the sample LO1CVD900 is approximately 65%.

[0061] The specifications of the materials produced after the CVD process, using the ultra-fine tailings as a catalyst, show that 900 °C is the best temperature for the growth of carbon nanostructures using methane as a carbon source. At this temperature there is the highest quality formation and amount of carbon nanostructures. Example 2 - Sandy Tailings

[0062] The basic composition, determined by X-ray fluorescence spectroscopy (FRX), of the sandy tailings sample is: 70% SiO, 9% Fe,03 and 11% Al,Os.

[0063] Unlike the ultra-fine LO1 tailings sample, according to the XRD analysis (Figure 5) and the Méssbauer analysis (Figure 6) the sandy tailings AO1 sample presents iron oxide only in the hematite phase. The heating of this material to 900 °C increased the crystallinity of the hematite phase and after the CVD process the iron oxide was converted into Fe® and y-Fe(C).

[0064] Like the LO1CVD900 sample, the sandy tailings sample submitted to the CVD process at 900°C {A01CVD900) also showed a higher proportion of graphitic carbon structures than the amorphous ones.

[0065] Figure 7 shows the TG curves (atmosphere air) for samples A01 and AO1CVD900. For sample AO1 small losses of mass near 200 °C are noted which should be associated with loss of hydration water. For material AO1CVDS00 we observe a discrete mass gain event at 450 °C, which is likely to be associated with the oxidation of Fe®, and a mass loss event around 600 °C, characteristic of organized carbon oxidation. The carbon deposited in these sandy tailings sample is believed to be more graphical than the carbon deposited in the ultra-fine tailings sample. Finally, according to thermal analysis, the carbon content in the sample AO1CVD900 is approximately 40%. The lower carbon deposition in the sandy tailings sample was already expected due to its lower Fe content, when compared to that of sample L01CVD900.

[0066] Through the tests performed, it was observed that the heating of the material up to 900 °C increased the relative intensity of the hematite peaks compared to those of silica. Example 3 - Magnetic separation process

[0067] The magnetic separation tests were performed for materials obtained after the CVD process and after reduction. For the sandy tailings sample, AO1CVD900, observing the magnetic and non-magnetic fractions, it was possible to notice white particles, indicating the presence and separation of the silica phase, which reported to the non- magnetic fraction. The white particles were analyzed by scanning electron microscope (SEM), which indicated the presence of silicon only, as Figure 8 shows. The thermogravimetric curves (Figure 9) indicated a carbon enrichment in the magnetic fraction of AO1CVDI00. Therefore, it was possible to conclude for the feasibility of using magnetic separation to separate Si-Fe / C.

[0068] After the tests, it was concluded that ultra-fine and sandy tailings, which are generated in large volume in the iron mining process, can react with CH4 at 900 °C to produce a composite formed by carbon nanofibers in a silica / aluminum matrix. The materials obtained have a carbon content of between 40-67% and high oil adsorption capacity in aqueous media. The application of a material containing basically iron and carbon can be done in some strategic sectors, as in iron ore pelletizing in mining and pig iron production in the steel industry. However, the use of these materials in these two sectors requires a minimum amount of aluminum oxides and silicon. For the manufacture of iron, for example, ideal quantities of 0.5-2.3% alumina and 4.5-6.0% silica are established for entry into the blast reduction furnaces. That's because a high proportion of alumina and silica increases the temperature of the sintering process of raw pellets and decreases their mechanical resistance by causing a more irregular structure of the pores.

[0069] One of the most common separation processes in the mining chain is magnetic separation. The magnetic separation tests and the characterization of magnetic and non-magnetic fractions show that this is a promising process for obtaining Fe / C separated from other elements from the tailings, such as silica and alumina, for a possible application of these materials in strategic sectors such as mining and steelmaking.

[0070] Thus, although only some modalities of this invention are shown, it is understandable that several omissions, replacements and changes can be made by someone skilled in the art, without departing from the scope of this invention. The modalities described should be considered in all respects only as illustrative and not restrictive.

[0071] It is expressly provided that all combinations of elements that perform the same function substantially in the same way to achieve the same results are within the scope of invention. Replacements of elements from one to another modality described are also fully claimed and contemplated.

[0072] It is also necessary to understand that the drawings are not necessarily in scale, but that they are only conceptual in nature. The intention is therefore to be limited, as shown by the scope of the attached claims.

Claims

CLAIMS 1. Process to obtain an iron / carbon-enriched fraction from the growth of carbon nanofibers in mining tailings, characterized in that it comprises the following steps: a) drying one iron beneficiation tailing in a kiln at a temperature of 80°C for 24 hours; b) heat treating the tailing at a temperature of 500 to 1200 °C in the presence of a volatile carbon source atmosphere for 30 minutes to 6 hours; c) dispersing the treated tailing and perform mechanical shaking of the treated tailing for 1 to 60 minutes; d) performing magnetic separation by bringing a magnet close to the outer surface of the vessel containing the dispersion of the material in water, for 1 to 30 minutes; e) separating the magnetic fraction, rich in iron and carbon, from the non- magnetic fraction, rich in silica and other chemical compounds; and f) drying the two fractions obtained, wherein the iron ore processing tailings contain have an iron content greater than 5%, wherein the volatile carbon source is selected from the group comprising methane, ethane, ethylene, propane, propene, butane, butene, pentane, pentene, hexane, hexene, benzene, toluene, xylene, naphthalene, decalin, methanol, ethanol, propanol, butanol, acetaldehyde, formaldehyde, propanal, butanedial, methyl acetate, ethyl acetate, ethyl propanoate, isopropyl propanoate, butyl ethanoate, methyl-propyl ketone, propanone, pentanone, hexanone and acetonitrile.

2. Process, according to claim 1, characterized in that the heat treatment of step b) occurs in the presence of the volatile carbon source and H; atmosphere.

3. Process, according to claim 1 or 2, characterized in that the step (b) is carried to a gas flow between 10-400 mL / min from the volatile carbon source.

4. Process, according to any one of claims 1 to 3, characterized in that the iron ore beneficiation tailings comprise tailings from iron mining slurry, sandy tailings, laterite, gangue, mining waste.

5. Process, according to any one of claims 1 to 4, characterized in that the dispersion of the materials referred to in step ¢) can be carried out either dry or wet.

6. Process, according to claim 5, characterized in that the wet dispersion of materials uses solvents selected from the group comprising water, ethanol, acetone, hexane, acetonitrile, methanol, propanol, butanol, isopropyl alcohol, ethyl acetate, chloroform.

7. Process, according to any one of claims 1 to 6, characterized in that the magnetic separation can be performed by two processes, ultrasonic and ultrasound- free, or a combination of them.

8. Process, according to any one of claims 1 to 7, characterized in that the magnet referred to in step d) is selected from the group comprising iron magnet, neodymium magnet, samarium cobalt magnet, alnico magnet and rare-earth magnet.

9. Process, according to any one of claims 1 to 8, characterized in that the magnetic separation referred to in step e) can be performed on a drum magnetic separator, carousel, high gradient, wet or dry. VALE S.A. UNIVERSIDADE FEDERAL DE MINAS GERAIS Patent Attorneys for the Applicants / Nominated Persons SPRUSON & FERGUSON

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