minerals Article Proposal for an Environmentally Sustainable Beneficiation Route for the Amphibolitic Itabirite from the Quadrilátero Ferrífero-Brazil Gizele Maria Campos Gonçalves 1 and Rosa Malena Fernandes Lima 2,* 1 Mine Planning at Brucutu Mine—Vale, São Gonçalo do Rio Abaixo, Rio de Janeiro CEP 35.935-000, Brazil; [email protected] 2 Mining Engineering Department, School of Mines, Federal University of Ouro Preto, Ouro Preto 35400-000, Brazil * Correspondence: [email protected] Received: 27 July 2020; Accepted: 4 October 2020; Published: 10 October 2020 Abstract: The high world demand for iron ores opposed to the rapid exhaustion of high-grade deposits from the main producing regions around the world has motivated the search and/or improvement of beneficiation routes, which enable the economic use of iron formations previously considered marginal ores, which have the potential to considerably increase mineable reserves due to their large volume. In this study, a sample of amphibolitic itabirite from the eastern region of the Quadrilátero Ferrífero, minas Gerais, Brazil was characterized, aiming at its use in the industrial pelletizing circuit. The main physical characteristics of this ore are moisture = 10% and specific weight = 3710 kg/m3. The ore has a high grade of loss on ignition—LOI (6.7%) and P (0.14%). Through X-ray diffractometry (XRD), optical microscopy and scanning electron microscope—SEM, the ore was found to consist of 64.5% goethite (amphibolitic, alveolar, massive and earthy); 6.8% hematite (martitic, granular and lamellar) and 0.9% magnetite. The main gangue mineral is quartz (25.5%). Based on the results of concentration tests (magnetic and flotation) performed with the studied sample, the magnetic concentration route of deslimed sample followed by the addition of slimes in magnetic concentrate can be incorporated into the pelletizing process. Keywords: amphibolitic itabirite; goethite; iron ore; magnetic concentration; flotation 1. Introduction Iron ore is the second-most traded mineral commodity on the market, mainly for the manufacture of cast iron and steel (98% of the world production) [1–3]. It corresponds to 15% of the products exported by Brazil, which stands as the third-largest iron-producing country and holds 12% of the world reserves, located mainly in the provinces of Quadrilátero Ferrífero, minas Gerais (MG) and Carajás, Pará (PA) [4,5]. The exhaustion of high-grade iron ore deposits from the main producing regions, located in Brazil, Australia, India and others, coupled with increased demand in the world market and increasingly severe environmental restrictions, have imposed a great challenge for the mineral industry. This current situation implies the development of beneficiation routes for marginal ores, aiming at greater metallic recovery and the minimization of tailings disposal, as well as the reprocessing of tailings deposited in dams, with Fe grades greater than 30%, to obtain products within the specifications for the steel industry [6,7]. Mineralogical compositions of slimes from desliming operations of industrial flotation circuits of Brazilian iron ores have a high proportion of goethite (in some cases, >50%), followed by martitic hematite; quartz and smaller proportions of magnetite, kaolinite and gibbsite. The Fe Minerals 2020, 10, 897; doi:10.3390/min10100897 www.mdpi.com/journal/minerals Minerals 2020, 10, 897 2 of 13 grades of this material are between 30–53%. Silva and Luz [8] carried out the magnetic concentration of a slime thickener underflow sample (100% 150 µm, with grades of 32.9% Fe, 37.7% SiO , 5.3% − 2 Al2O3 and 5.7% loss on ignition—LOI)) from a mine located in Quadrilátero Ferrífero. The magnetic field intensities tested were of 0.6, 0.9 and 1.2 T. The best result after a cleaner step was obtained with a magnetic field of 1.2 T: 64.6% Fe, 5.5% SiO2 and a mass recovery of 62.8%. For an underflow sample of slime thickener from the Brucutu mine (46% Fe, 15% SiO2, 10% Al2O3 and 10% LOI), there was obtained a concentrate with 66.8% Fe, 0.8% SiO2, 0.97% Al2O3 and 2.4% LOI for a magnetic field of 1.45 T. however, the mass recovery was very small (12.7%), due to the fine size distribution of the sample (d80 = 10 µm) [9]. Different processes of metamorphism and weathering of iron formations in the different geographical regions of Quadrilátero Ferrífero led to the formation of different typologies of ores, which are classified as compact, semi-compact and friable itabirites, according to the percentage retained in a given mesh. The grades of Fe in these ores vary between 30% and 60%. At the western edge of Quadrilátero Ferrífero, compact itabirites comprise a percentage retained >55% +6.3 mm, semi-compact (between 30% to 55% +6.3 mm) and friable (<30% +6.3 mm) [10]. At the central and eastern portions, there are a predominance of friable ores, and among them, there are the amphibolitic (~1.2% Al2O3, p > 0.14% and LOI > 5%) and aluminous itabirites (Al2O3 > 3.0% and LOI > 3%) of Alegria’s (60% 0.15 mm) and Brucutu’s (80% 8 mm) deposits [11,12]. These ores have − − a high proportion of goethite, generating large amounts of slimes, which cause problems both in the concentration by flotation and in the dewatering stages (thickening and filtration). For this reason, they are considered marginal or, depending on their grade, they are used as a natural fine sinter feed [11–13]. In this study, a characterization (physical, chemical and mineralogical) was carried out on a sample of amphibolitic itabirite (marginal ore) from the eastern region of the Quadrilátero Ferrífero, which corresponds to 15% of the current reserves (263 million tons) of Brucutu [13], aiming at the development of an adequate processing route to obtain a concentrate of this typology of ore to be incorporated into the industrial pelletizing process. 2. Materials and Methods The amphibolitic itabirite sample used in this study was obtained by the composition of two subsamples: A1 (28 kg, 55.8% Fe) and A2 (52 kg and 41.2% Fe). These were collected in two different regions of amphibolitic itabirite in Brucutu’s deposit (Figure1), aiming at obtaining a Fe grade (~46%), compatible with ore grades current feed in industrial concentration plants in Quadrilátero Ferrífero [6,11,14], since the friable ores with grades higher than 50% Fe can be used as a natural fine sinter product [13]. As seen in Figure1, the ore has an ocher color and a clay appearance. Figure 1. Geological section and map of Brucutu’s deposit, with the location of the two regions where the subsamples A1 and A2 (right side) of the amphibolitic itabirite were collected. After the homogenization of the amphibolitic itabirite sample ROM (run of mine), aliquots were removed for physical characterization: moisture determination, specific weight and size distribution; chemical: determination of FeTotal, SiO2, Al2O3, CaO, MgO, MnO, Fe3O4, P and LOI grades and mineralogical: mineral phases identification and determination of the quartz’s liberation. Minerals 2020, 10, 897 3 of 13 After determining the ore’s liberation mesh, a part of the sample was comminuted at 105 µm for − exploratory concentration tests. 2.1. Physical Characterization The natural moisture (wet basis) of the ore sample was performed in a furnace at 100 C( 5). ◦ ± The specific weight (average of the values obtained by 3 scans) was determined by the Quantachrome Corporation pycnometer Ultrapyc 1200e/UPY-30 model (Boynton Beach, FL, USA) in accordance with the methodology of Silva et al [3]. The determination of the ore’s size distribution, carried out in duplicate, was achieved through wet sieving (sieves from 8000 to 45 µm) and a laser particle size analyzer (fraction 45 µm), CILAS − 1180 model, used under the following conditions: 60 s of ultrasound, 25% obscuration and the addition of 10 drops of sodium hexametaphosphate at 1% w/v to disperse the suspension. 2.2. Chemical Characterization and Loss on Ignition (LOI) The ROM sample’s grades of FeTotal, SiO2, P, Al2O3, MnO, MgO, TiO2 and CaO, by size fraction, as well as the concentration tests products, were determined by X-ray fluorescence—XRF (Rigaku X-ray spectrometer Simultix 14 model, Rigaku, Osaka, Japan). For this, fused pellets were made at 1000 ◦C of a mixture consisting of 1 g of each pulverized sample ( 38 µm) and 5 g of lithium tetraborate/metaborate − (67% Li2B4O7/33% LiBO2). The Fe3O4 grade (1.3 g samples) was determined by Rapiscan’s Satmagan 135 equipment (Rapiscan, Skudai—Johor, Malaysia) according to the methodology described by Breuil et al. [15] and Stradling [16]. The experimental procedure for determining the loss on ignition (LOI) consisted of introducing the sample (150 g) in a muffle furnace, regulated at a temperature of 1000 ◦C, where it remained for 1 h, and the loss on ignition calculation was determined by the percentage of sample mass loss after calcination in relation to the initial mass. 2.3. Mineralogical Characterization X-ray diffractometry—XRD (total powder method) was used to identify the mineral phases of the studied sample. For this, a PaNalytical model X’pert3Powder diffractometer (Malvern Instruments, Malvern, UK) equipped with a Cu tube (λCu = 1.5405 Å) and Ni filter was used. The operation conditions were: 45 kV and current of 40 mA and scanning angle (2θ) from 5◦ to 90◦ counting time of 15 min. The data were collected by using the X-ray Data Collector software (version 5.4). mineral phases identification in the X-ray diffraction pattern was performed by the software highScore Plus (version 4.5), using the standard database X-ray patterns of the ICCD PDF-2, 2015. Thermogravimetric analysis was used to confirm/identify the hydrated mineral phases present in the sample.