Resumo em Inglês:

Abstract This article presents an experimental study performed to evaluate the volume of material released from the reservoir during a tailings dam failure event using models. To verify the influence of the parameters related to the breach geometry and the undrained shear strength (Su) in a failure event, 20 scenarios were simulated considering the absence of water in the reservoir. The material used to simulate tailings was bentonite, due to the similarity between the properties of the mud and mineral tailings sludge. Geometry and undrained shear strength were adjusted considering a scale factor of 1: 500. Regarding the studied parameters, the geometry of the breach was based on data from literature, whose lateral slopes were 0.50 H: 1V, 0.51 H: 1V and 0.5467 H: 1V in the trapezoidal breaches and 1: 1 (L / H = 0.97) and 1: 1 (L / H = 1.1) in the rectangular ones. The undrained shear strength ranged from 0.030 to 0.20 kPa. The results allowed to conclude that the mobilization of material increases with the average aperture width of the trapezoidal breach, being this the distinct behavior in rectangular breaches. Although the rectangular breaches had smaller average widths compared to the trapezoidal breaches, their base widths were larger and it is possible to infer that the mobilized volume depends on the geometry and the average width of the breach.

Resumo em Inglês:

Abstract This study explores the potential of the granite residue to be applied as a supplementary cementitious material. Furthermore, the efficiency of grinding methods in the improvement of the residue reactivity was also evaluated. The granite residue was collected in a facility located in Brazil and used as a Portland cement replacement with a substitution rate of 25% in mass. The residue was submitted to wet, dry and additive dry grinding methods, with several different times. The cement-based composites were characterized by quantitative X-Ray diffraction using the Rietveld's method, thermogravimetric analysis, and compressive strength. In conclusion, there was observed a higher efficiency of the wet grinding method, followed by an increase in compressive strength results as grinding time increased. Furthermore, the portlandite content was lower in the cement-based composite with granite residue, especially in the samples ground for 60, 120, and 180 minutes; a fact that summed up with other results for the pozzolanic potential of the granite residue.

Resumo em Inglês:

Abstract The inelastic second-order behavior of steel structural columns under minor-axis bending is presented in this article. To study this behavior, a nonlinear frame element formulation is adopted in which the steel's plasticity process is accompanied at the nodal points of each finite element through the refined plastic-hinge method (RPHM). A tangent modulus approach is employed in order to consider the stiffness degradation in function of the internal forces' variation, and the second-order effects, residual stresses and geometric imperfections are considered in the modeling of column behavior. As a criterium for defining the ultimate limit state of the column cross-section, strength surfaces are adopted. These surfaces describe the interaction between the axial force and bending moment (N-M interaction diagrams). To solve the nonlinear equilibrium equation for the structural system, the Newton-Raphson method is used, coupled with continuation strategies. Columns with different slenderness, boundary and loading conditions are analyzed, and the results obtained are comparable to those found by other researchers. The results lead to the conclusion that the numerical approach adopted in this study can be used for a better behavioral understanding of the steel column under weak-axis bending.

Resumo em Inglês:

Abstract This article reports on a preliminary investigation about the effect of concentrated transversal force on the bending moment resistance of rectangular hollow steel section (RHS) beams. Two six-meter-long specimens with yield strength of 300 MPa and cross-section size of 250×150×6.4 mm were subjected to bending tests using a four-point load configuration. A three-dimensional nonlinear finite element model was developed by using the software ABAQUS to simulate the flexural behavior of the RHS beams. The model was validated against the experimental results and subsequently used to conduct a parametric study. The investigated parameters were the force application method and the corner radius between the webs and the flanges of the rectangular tube. The results showed that RHS beams may undergo failure due to large localized plastic deformations beneath the concentrated force, whenever this force causes compression on the webs. The use of a doubler plate on both webs can significantly reduce the detrimental effect on the bending moment resistance. Moreover, the effect is shown to be more pronounced for rectangular hollow steel sections with larger corner radius.

Resumo em Inglês:

Abstract The Santa Rosa Pegmatite Field (SRPF), in northeastern Minas Gerais State, is one of the most important gemstone sources in Brazil. The economy of several neighboring cities greatly relies on the trade of its gemstones. However, efforts to improve gemstone mining with practical, scientific methods are scarce, making it a yet inexpensive, marginally profitable practice. In this scenario, it is opportune to encourage new approaches to optimize mining in pegmatitic deposits. This study looked into the case of a tourmaline dig in the city of Franciscópolis, near Teófilo Otoni. The pegmatite has a weakly zoned structure, and was formed during the final stages of the Neoproterozoic Araçuaí Orogeny, associated with the intrusion and crystallization of the Santa Rosa Granite. GPR profiles were executed to locate structural anomalies inside the rock and its contacts with the host rock, and mineral samples were characterized based on compositional data obtained from ICP-MS and microprobe analyses. The results provided useful information that enabled the creation of a tridimensional digital model of the dig and the pegmatite dike, and may guide future operations in the dig. In the future, the proposed methodology may be applied to more cases to generate a database of geological information that, in addition to the economic scope, could lead to a better understanding of the local granite-pegmatite systems.

Resumo em Inglês:

Abstract The definition of geological domains is essential for mineral exploration and is traditionally done manually, section by section, in a laborious, time consuming and subjective process, to construct a 3D model. The technique referred to as implicit modeling is an option to model deposits in a fast and practical manner. This article presents the lithological model of the Horto-Baratinha iron deposit, located in the Antônio Dias municipality, central-eastern part of Minas Gerais state, constructed using the Leapfrog Geo® software. The deposit is situated at the Guanhães tectonic block that is a basement domain of the Neoproterozoic Araçuaí Orogenic Belt. The deposit is comprised of itabirite-hosted high-grade iron bodies (>60 wt.% Fe) associated with polydeformed mica schists, amphibole schist with a Statherian maximum deposition age, enclosed by Statherian granitoids of the Borrachudos Suite and crosscut by undeformed pegmatite dikes crystallized during Late Ediacaran-Cambrian. The sequence was affected by progressive multiple deformation phases, associated with the collisional stage of the Brasiliano Orogeny (630-560 Ma), generating a dome and basin mesoscale refolding shape. The model points the proximity between high-grade bodies and pegmatite indicating the possibility that the intrusions contribute to the iron mineralization.

Resumo em Inglês:

Abstract Estimating mineral resources of a stratiform mineral deposit is not always a simple activity. Some difficulties can arise in mineral deposits where the thickness is relatively much smaller than the dimensions in the horizontal plane, or because these deposits have suffered events after their genesis, such as thrusts and folds. Usually, in these cases, we use a new variable named accumulation as a product between the average grade and thickness. Then, from these service variables, accumulation and thickness are estimated in a regular grid. Dividing accumulation by thickness, we have the mean grade. However, the mean grade is just an approach because the uncertainties of variables are not considered in this division. This calls for applying the Taylor series to computing, not only the mean grade, but also the associated uncertainty. In this article, we present the satisfactory results of this method applied to quantify the mean grades and uncertainties of the blocks to a stratiform phosphate deposit located in southern Mato Grosso, Brazil.

Resumo em Inglês:

Abstract Reactivation of a landslide is usually accompanied by microseismic signals emitted from the deforming soil mass. The reproduction of similar signals in a physical model test conducted under control conditions can allow researchers to explore and test such complicated signals to improve the prediction of full-scale failure. The present study investigates the similarity between the slidequakes (microseismicity) naturally emitted from an existing colluvial landslide (Sobradinho, Brazil) in response to rainfalls and the emissions generated by a pullout test of an expander body (EB) pile in tropical soil under controlled conditions. The microseismic signals emitted from both experimental sites (i.e. the landslide and the EB pile test) were recorded and compared. Data were acquired by mini-arrays of four short-period seismometers. For the signal nomenclature, a typological scheme was adopted, in which sonograms/spectral contents of the signals were used. As a result, short duration microseismic signals were observed during the pullout test. In contrast, at the Sobradinho landslide, the testing detected signals of different characteristics whose source mechanisms have remained ambiguous, mainly because of the short duration of the data campaigns. However, at the landslide, propagating events were observed that might be attributed to the energies generated by the river bedload during the heavy rains. The present study offers some insight into the pre-collapse dynamic behavior of unstable slopes in clayey formations.

Resumo em Inglês:

Abstract Aluminum bronze alloy is applied in environments that require materials of high mechanical resistance and wear, such as marine, oil & gas and aerospace ones. This study analyzes the densification of composites based on aluminum bronze with additions of the vanadium (VC) and niobium (NbC) carbides, and the influence of these carbides in the milling efficiency and improvement of the diffusion process between particles to obtain better results for density and porosity. The composites were produced by powder metallurgy from aluminum bronze powders obtained from the mechanical milling process of discarded scraps. The efficiency of the sintering process depends on parameters, such as the time and temperature of sintering, together with the size of the particles obtained from the milling process. This study aimed to obtain and characterize the composites produced by the powder metallurgy route, with NbC and VC addition and to analyze physical properties, such as density and porosity. The powder morphologies, particle sizes and samples sintered were performed by scanning electron microscopy (SEM), X ray diffraction (XRD), laser diffraction analysis and optical microscopy (OM). The results indicate that addition of VC improves the milling efficiency, when compared to NbC addition, since it promotes a greater reduction of the particle size, directly favoring the sintering process. In this case, to achieve similar particle size, twice the milling time was required when NbC was used. The density values achieve ~ 73% of reference material for VC addition and ~ 68% for NbC and porosities varying between 27% and 38%.

Resumo em Inglês:

Abstract Researches of polymer blends based on biological and biodegradable polymers appear as a viable alternative to develop environmentally friendly materials. Therefore, the aim of this research was to produce compounds made with biological polyethylene, i.e., Biopolyethylene, Bio-PE, added to the biodegradable Polycaprolactone (PCL) and functionalized by the copolymer of polyethylene grafted with acrylic acid (PEgAA), to obtain better mechanical properties and toughen Bio-PE. Compounds were processed in a co-rotating twin screw extruder and sample tests were injection molded. The compositions investigated were: Bio-PE/PCL at 90/10, 80/20 and 70/30 wt.% without compatibilizer and upon addition of 10 phr (parts per hundred of resin) of PEgAA. The blends were characterized by X-ray diffraction (XRD), impact strength, heat deflection temperature (HDT) and scanning electron microscopy (SEM). Through XRD, it was observed that addition of PCL and PEgAA did not significantly change Bio-PE diffraction patterns. Impact strength data showed that the blends presented a tougher behavior upon addition of PCL and PEgAA. The HDT of compatibilized blend with 20wt.% of PCL was slightly higher. SEM images of compatibilized blends showed lower average particle diameters as well as absence of coalescence and aggregates.

Resumo em Inglês:

Abstract The aluminum alloy AA 6351 is a precipitation hardened alloy of the Al-Mg-Si system, additionally containing Mn and Fe. In this study, the microstructural characterization during processing of a thick wall extruded AA 6351 tube was carried out. Several complementary techniques for microstructural characterization were used, such as polarized light optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, backscattered electron diffraction, X-ray diffraction, hardness and electrical conductivity measurements. The main characteristics of the grains and precipitates were analyzed. After solidification, the presence of a relatively homogeneous grain distribution with an average diameter of about 100 µm and an intermetallic phase with elongated morphology rich in Al, Fe, Mn and Si was observed. During extrusion, the initial grain size was reduced to about one-fifth of the initial diameter and the elongated phase, probably a-Al(Fe,Mn)Si, was fractured and redistributed and the resulting fragments were aligned in the extrusion direction. A peripheral coarse grain zone was detected and analyzed near the outer and inner surfaces of the tube.

Resumo em Inglês:

Abstract Cyclic softening and hardening processes are expressed by the change in the stress amplitude necessary to cause a given strain amplitude. Understanding the cyclic stress-strain behavior of materials is an important step in the complex study of their fatigue behavior. The potential differences between the defect structures of cold-formed materials may also be related to internal stress changes. Considering that wiredrawing and rotary swaging apply distinct forces on the material in order to obtain the product, differences may arise in the defect structures that can, consequently, affect its mechanical behavior. This study aims at evaluating and comparing, by means of strain-controlled fatigue tests, the cyclic behavior of polycrystalline electrolytic copper cold-formed by wiredrawing (WD) and rotary swaging (RS) with 87% area reduction. The fatigue test results evidenced the highest resistance to cyclic deformation presented by WD material in the low cycle regime. It was observed that the strain hardening for both cold forming conditions is related to a great increase of long-range stresses in the defect structure and the cyclic softening is related, mainly, to the subsequent drop of that stresses. The WD internal stresses resulted slightly bigger than those of the RS condition.

Resumo em Inglês:

Abstract Radial basis functions can be used as an alternative method for mineral resource estimation when ordinary kriging cannot be done because it is impossible to calculate an experimental variogram. Interpolation based on radial based functions is a method that is similar to ordinary kriging. In this context, this article presents the results of gold resource estimation and modeling of the União Luis and Morro do Carrapato gold deposits located in Alta Floresta Gold Province, Mato Grosso. Experimental variograms in the main direction (90-degree strike) resulted in a pure nugget effect, whereas in the orthogonal direction (180/85), they resulted in a structured variogram. However, the structured variogram for 180/85 is useless because three orthogonal variograms are needed to define the anisotropy ellipsoid for deriving a correlation model used in ordinary kriging. Thus, mineral resource estimation was done using multiquadric equations, a very popular radial based function kernel. The 3D model for gold grades showed a vertical distribution suggesting a structural conditioning for gold mineralization. The grade-tonnage curve with a simulated cutoff of 5.0 g/ton resulted in a gold mineral resource of 2.122 tons. Through the above, the gold estimation and multiquadric equation-based 3D model for the studied area can be considered effective in its objective to estimate ore resources from the available data.

Resumo em Inglês:

Abstract Quartz floatability in cationic reverse flotation depends on the suitable choice of surfactant type and the conditions under which they are applied. The design of experiments (DOE) allows the evaluation of process variables, in a structured and independent way, with statistical validation and a limited number of tests. Tests of microflotation of quartz, in the size range -150 +75 µm, using factorial design of experiments, showed that etherdiamine leads to higher level of quartz floatability than ethermonoamine, favored by increase in collector concentration, at the high level of pH tested (11.0). Floatability values above 90% were achieved with the use of 3 mg/L of ether diamine for both pH levels, while with ether monoamine the target was reached only at pH 11.

Resumo em Inglês:

Abstract The aim of this research is to investigate the liquefaction susceptibility of silt sandy mining tailings by experimental laboratory techniques. The main aspect analyzed is how techniques of sample reconstitution impact the results obtained in static undrained triaxial tests. Different methods of sample preparation are reviewed, such as moist tamping (MT), air and water pluviation, and a newly developed one called the Slurry Deposition (SD) method. This research highlights the importance of the "fabric" or particle structural arrangement associated with the various specimen preparation techniques when liquefaction potential assessment is of concern. Two series of undrained static triaxial tests were performed on specimens prepared according to MT and with SD techniques on specimens in the loose and very loose state. Results have demonstrated that MT specimens have shown the whole spectrum of liquefaction resistance (total liquefaction, limited liquefaction, and no liquefaction) on increasing density, while the SD campaign has shown only liquefaction resistance even in the overlapping intermediate densities with the MT series, where the latter has shown liquefaction, although limited. This scientific study critically discusses the risk of taking laboratory results of replicated soil elements that may not correspond to the reality.

Resumo em Inglês:

Abstract The main coal seams explored in the coal region of Santa Catarina are Barro Branco (BB) and Bonito (BO). Owing to the association with the mineral matter, the tailings generated in the beneficiation are arranged in disposal areas, and subject to the generation of acid mine drainage (AMD). The objective of this study was to evaluate the use of pyrite present in the coal rejects of the BB and BO seams and the environmental gains with desulfurization. For this purpose, densimetric separability test, ash, sulfur, and AMD generation analyses were performed. In addition, the amount of pyritic concentrates and sulfuric acid were estimated considering the current level of production. Three densimetric fractions were obtained: less than 2.2 (energetic material), between 2.2 and 2.7 (low sulfur material), and greater than 2.7 g cm-3 (pyrite concentrate). The results revealed that the two seams could be beneficiated by gravimetric processes, obtaining pyrite concentrates with approximately 60% pyrite. By converting pyrite to sulfuric acid would represent an increase of 500,000 tons per year in the Brazilian production of this material and, in environmental terms, a reduction of up to 90% of the acidity potential to be disposed in the environment in the case of the BB seam and 65% for the BO seam. It was also observed that the “desulfurized” fraction of the BO had higher levels of pyrite and a higher potential for acidity generation than the BB seam, implying greater risks of environmental contamination and higher acid water treatment costs.

Resumo em Inglês:

Abstract This research proposes a new approach to recommend a responsible mining guideline on how to secure a social license to operate in Ondo state, Nigeria for oil sands mineral resources taking into account the bituminous natural effects. This is the case of bituminous oil sands in Southern Nigeria, where warm weather can induce the emission of natural bitumen fumes. Because this emission may bring occupational exposure to the local communities, mining is perceived to be an opportunity for both social-economic improvement but also an efficient approach to reduce exposure to bitumen fumes. The study investigates the importance of the perception of the society about responsible mining practices in establishing a social license for a mining operation. The results of the investigation include an appraisal of the social status, living conditions of the communities, effects of pre-mining activities and the natural impacts of bitumen from oil sand on the community. The conclusions are that the bituminous natural effects on the communities can facilitate the approval of SLO, if the company can fulfil its promises, as mining is perceived to be a welcome solution to the problems posed. In addition, the mining company must also be transparent with the community as this changes the perception of society about responsible mining practices and help in establishing SLO.

Resumo em Inglês:

Abstract Not long ago, certain iron ore processing plants in Brazil were unable to efficiently recover iron ore fines and, as a result, operated only with high grade iron ore. For this reason, material stored in some iron ore tailings dams have considerable amounts of iron content with a potential to produce pellet feed fines through a concentration process. This study presents the results of magnetic concentration tests carried out on samples from four iron ore tailings dams located in Minas Gerais, named as A, B, C and D. The average iron content is 54% for A dam, 36% for B dam, 49% for C dam, and 58% for D dam. This material had a significant amount of ultra-fine particles, with more than 50% below 0.045mm for all dams, particularly the A and D dams, which present more than 80% of the below 0.045mm on average. Magnetic concentration tests were conducted on bench and pilot scales. The resulting concentrates showed the following average iron content: 66% for dam A, 63% for dam B, and 67% for dams C and D, with a mass recovery of 42% for dam A, 38% for dam B, 75% for dam C, and 63% for dam D. These results confirm the potential for pellet feed production from tailings dams through magnetic concentration.

Resumo em Inglês:

Abstract Comminution represents a large portion of the capital and operating cost of a mineral processing plant. In 1983, Cohen estimated that comminution processes could account for 30% to 50% of the power consumption of the mill, and typically represents 50% of the operating costs of a mine. Therefore, its optimization is directly related to reduction of these operating costs. Among the crushing equipment, the hammer mill is one which is dedicated to operations that aim for a high reduction ratio with the controlled generation of fines. This crusher is recommended for friable and low abrasive ores presenting a high productive capacity. This study aims to develop a stepwise approach that allows the use of the classical crusher model (Whiten-Andersen) in modeling and simulation of circuits containing a hammer mill, simulating the resulting product according to variation of rotation speed within the equipment. The existing model for crushers developed by Whiten-Andersen considers the Perfect Mixing Model, which represents crushing through equations related to selection and breakage functions, that provide an equilibrium condition. This study aims to develop a stepwise approach that allows the use of the classical crusher model in modeling and simulation of circuits containing a hammer mill, by simulating the effect that the variation of rotation speed within the equipment implies in the generated product. The comparisons between the experimental and simulated data indicated that the model fits the data for both, P80 values and percentage passing in 19.1 mm sieve. The model created was validated based on specific experimental campaign.

Resumo em Inglês:

Abstract A considerable portion of energy consumption and, as a consequence, operational costs in mineral processing, is associated with comminution. High Pressure Grinding Rolls (HPGR) are appealing for their energy efficiency and resulting lower operating costs. This article evaluates this technology as an alternative to the conventional fused alumina comminution route of a specific plant comprising a complex roll crushing circuit. Two fused alumina samples, called BT and TB, were submitted to HPGR (open circuit) and physical characterization (DWT, BBWI, bulk density, specific gravity) tests. In addition, simulations were conducted using JKSimMet® 6.0 software, aiming to predict the performance of a closed circuit equipment and scale-up of an industrial-scale unit. Product size distributions of the open circuit HPGR tests and closed circuit HPGR simulations were compared with the product size distribution required by the industrial comminution circuit. The required throughput was also evaluated. Results show that the alternative HPGR route provides a remarkable potential for circuit simplification, while considerably reducing the number of comminution equipments from 13 to 1, which facilitates operational control and possibly reduces operating costs.