Scielo RSS <![CDATA[Rem: Revista Escola de Minas]]> http://www.scielo.br/rss.php?pid=0370-446720160002&lang=pt vol. 69 num. 2 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[Editorial]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200129&lng=pt&nrm=iso&tlng=pt <![CDATA[A stochastic approach for the wind load effect on steel structures]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200137&lng=pt&nrm=iso&tlng=pt Abstract The Brazilian design load standard still provides a wind speed map developed in 1977. Since then, new data have been collected and new charts have been proposed in literature. The literature not only alerts to changes in short-term wind gust patterns, but it also warns that the wind speed values are higher than observed in the past. Many researchers have suggested that these differences are correlated to climate change effects. Besides the geophysical and societal impacts of climate change, there is a general concern between designers on the impacts of higher wind speeds on structural design. This paper aims to analyze the wind speed as a stochastic variable and its influence on the design of steel structures when changes in wind speed occur. A stochastic approach is used to evaluate expected stress values for a steel beam-column example. A Monte Carlo analysis is performed on a forty-story steel frame to compare the impact of different wind speed scenarios and types of analysis. In the analyses, the wind speed is approached by a Gumbel distribution and future wind scenarios are generated for sensitiveness evaluation. The analytical and Monte Carlo analyses indicate that greater attention shall be given to the consequences of using an average wind speed value instead of a probability distribution function. <![CDATA[Surface drainage system for dry docks in shipyards - Case study of Estaleiro Rio Grande (Technical Note)]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200147&lng=pt&nrm=iso&tlng=pt Abstract This study aims to present a methodology for the design of a surface drainage system for dry docks in shipyards, taking into account the rainfall intensity at the site, the damping capacity of the hydraulic structures (drainage channels) and the pumping capacity of the pumping system. A case study of a dry dock owned by Estaleiro Rio Grande, located at the state of Rio Grande do Sul, is presented. The results obtained indicate alternatives for channel and submersible pump sizing. These pumps would be used to control the dry dock flooding after an intense rainfall event. <![CDATA[Analisys of hot deformation behavior of super duplex stainless steel UNS S32760 through processing maps]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200155&lng=pt&nrm=iso&tlng=pt Abstract The need for materials with higher strength and corrosion resistance in corrosive environments, such as in the oil extraction in saline media, has led to the use of super duplex stainless steels in projects such as the Pre-sal. The manufacture of these materials involves the step of thermomechanical processing, whose performance depends on the workability of the material. Processing conditions in which the super duplex stainless steel UNS S32760 can be worked safely and in which the material can fail were investigated in this presentation. The physical simulation was performed by means of hot torsion testing. The tests were performed at temperatures ranging from 900°C to 1200°C and strain rates of 0.01s-1 to 10s-1. The evolution of strain rate sensitivity of flow stress (m) for deformation of 0.5 at all temperatures investigated here was determined. After attaining the values of m for each deformation condition, the values of the power dissipation efficiency (η) were calculated, an instability criterion (ξ) was applied, and processing maps were constructed. Using these maps, the effects of deformation conditions on the power dissipation efficiency and the material plastic instability were discussed. The domains of processing maps, the observed microstructures and the shape of plastic flow stress curves were associated. <![CDATA[Strategies for corrosion inhibition of slurry pipelines prior to commissioning]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200161&lng=pt&nrm=iso&tlng=pt Abstract A practice used to prevent corrosion in buried slurry pipelines is the hibernation of pipelines with an aqueous solution containing corrosion inhibitors before beginning the mining operation. The aim of this work is to evaluate the corrosion resistance of API 5L X70 steel used in the slurry pipelines in hibernation solution containing sodium sulphite, sodium hydroxide and glutaraldehyde in a synthetic river water. The electrochemical techniques used are the Tafel analysis and electrochemical impedance spectroscopy. The synergistic effect of the components of hibernation solution on the corrosion resistance of the API 5L X70 steel was evaluated. A lower corrosion resistance was obtained for the API steel in aqueous solution of sodium sulphite, and in solution of sodium sulphite with glutaraldehyde. The hibernation solution was efficient in inhibiting steel corrosion but the highest corrosion inhibition efficiency was obtained with the glutaraldehyde aqueous solution. <![CDATA[Microstructural analysis in the Fe-30.5Mn-8.0Al-1.2C and Fe-30.5Mn-2.1Al-1.2C steels upon cold rolling]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200167&lng=pt&nrm=iso&tlng=pt Abstract Electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) were used to examine microstructural changes of the austenitic low-density Fe-30.5Mn-8.0Al-1.2C (8Al) and Fe-30.5Mn-2.1Al-1.2C (2Al) (wt.%) steels during cold rolling. As the strain increased, deformation mechanisms, such as stacking faults, slip, mechanical twinning, and shear banding were activated in both steels cold rolled up to strain of 0.69. Only slip was noted in these steels at low strain (ε=0.11) and slip dominance was detected in the 8Al steel at higher strains. Shear banding became active at higher strain (ε~0.7) in these materials. An inhomogeneous microstructure formed in both alloys at such strain level. More extensive mechanical twinning in the 2Al alloy than that in the 8Al alloy was observed. Fish bone-like structure patterns were revealed in the 8Al steel and a river-like structure in the 2Al steel. Detailed microstructure features as elongated and fragmented grains along the rolling direction (RD) were found for both steels, as already observed in other high-Mn steels. These deformed structures are composed by lamellar packets which can contain mechanical twins or slip lines and shear bands. <![CDATA[Damage evolution in a tensile specimen of a ductile stainless steel]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200175&lng=pt&nrm=iso&tlng=pt Abstract This paper presents a study about the fracture mechanism of a ferritic stainless steel (UNS S44400 type) during a tensile test. The applied materials for the experimental procedures were 25 specimens of the steel, machined in the rolling direction. Each specimen was submitted to standard polishing procedures. One of the samples, in the original state, was structurally characterized by reflected light optical microscopy. The other samples were submitted to tensile tests with a constant displacement rate. Three samples were tested until failure (complete tests) and the others just until specific strain values, when the tests were interrupted and the samples were characterized by using optical and scanning electron microscopy. The main objective of these characterizations was to evaluate the structural damage evolution and to identify the fracture mechanism for the tested conditions. A methodology to quantify the damage evolution by surface roughness, identified by optical microscopy, was proposed. A new index - Damage by Diffuse Reflection Index (DRI) - was proposed to quantify the damage evolution in function of the specimen deformation. It was possible to confirm the ductile behavior of the studied steel and that the main fracture mechanism was the traditional dimpled rupture. <![CDATA[Slope stability analysis at highway BR-153 using numerical models]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200185&lng=pt&nrm=iso&tlng=pt Abstract An existing cut slope on Highway RS-471/BR-153 is studied. The slope is composed of the Serra Geral Formation's material: a highly altered volcanic breccia and above it a slightly altered and very fractured rhyolite. A numerical analysis of the slope is carried out in two dimensions. Fracturing of the rhyolite necessitates the use of a constitutive model for materials with families of discontinuities (Ubiquitous-joint). To simplify the analysis of the problem and to examine some of the most sensitive variables, two more analyses are made, replacing the initial model by a Mohr's constitutive model, which considers the material as continuous. The results obtained from the Ubiquitous-joint model provide an acceptable representation of the field conditions, showing a failure mechanism type of rockfall from the face of the slope in the rhyolite, and the rupture surface of the breccia, without propagation of surface failure. In the analysis, when considering both materials as continuous, it is not possible to take account the fault conditions simultaneously, and this analysis also requires values of the mechanical parameters different from those recommended in literature. <![CDATA[Dispersion degree and zeta potential of hematite]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200193&lng=pt&nrm=iso&tlng=pt Abstract The dispersion degree of the mineral particles in the pulp is especially relevant regarding the performance of the cationic reverse flotation of iron ores. The gangue minerals should remain dispersed while hematite particles should be selectively flocculated. The present study addressed determinations of dispersion degree and zeta potential of hematite in the presence of different dispersants, classified as organic polymeric (natural and synthetic), organic monomeric, and inorganic. Special attention was paid to results achieved at pH 10, used in plant practice. For natural organic polymers, correlation was observed between the dispersion degree and the increase in the negative value of zeta potential. Some synthetic organic polymers enhance the dispersion of hematite particles despite not affecting significantly the zeta potential. Sodium silicates, irrespectively of the SiO2/Na2O ratio, at pH 10, did not impact significantly either the dispersion degree or the zeta potential. <![CDATA[Effects of hematite surface characteristicson filtration process]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200199&lng=pt&nrm=iso&tlng=pt Abstract In iron ore pelletizing plants a range of process parameters such as particle size distribution, specific surface area, and moisture, must be controlled to achieve optimized operation conditions. Particle size distribution and specific surface area are controlled during the grinding operations. Moisture, however, is controlled during filtration of the ground products. This work investigates the relationship between particle morphology, filter cake moisture and filter capacity. The samples were taken during the filtration tests and referred to three different blends presenting distinct mineralogical features and similar chemical compositions in order to investigate the effects of only the hematite surface characteristics. Six types of morphology are distinguished: granular hematite, tabular hematite, martitic hematite, polycrystalline hematite, hematite-goethite aggregates and goethite. For each filtration test, the filter cloth product was characterised. The characterisation analysis revealed that blends containing martitic hematite concentration above 11.45 percent increased substantially the filter capacity. However, it had also caused an increasing in final moisture content that reached values around 10.0 % compared with industrial moisture specification that can vary on the range of 8.5 to 9.5 %. <![CDATA[Modelling and Simulation of the Santa Rita Mine Milling Circuit]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200207&lng=pt&nrm=iso&tlng=pt Abstract The Santa Rita Mine, located in the State of Bahia, was the first Mirabela Mineração operation in Brazil. Started in 2009, the nickel sulphide processing plant has undergone constant modifications, aiming to adapt to the changes in the ore. Main modifications included autogenous grinding converted to semi-autogenous, as well as the installation of a desliming stage aiming to remove ultrafine minerals which reduced the nickel recovery in flotation. A full survey and ore characterization campaign was carried out to assess alternatives for increasing grinding circuit capacity. Experimental data were balanced and used to calibrate mathematical models which were the basis for simulation exercises. This paper describes the main aspects related to circuit modeling and simulation, as well as assessing alternatives for increasing the grinding circuit capacity. <![CDATA[Mine/Mill production planning based on a Geometallurgical Model]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200213&lng=pt&nrm=iso&tlng=pt Abstract The Pau Branco mine supplies two blast furnaces with iron ore lumps, and currently, charcoal consumption for pig iron production accounts for 47% of the blast furnaces' operational cost. A geometallurgical model is presented to support an economic study considering reserve volumes, product quality, and operational costs based on the metallurgical performance of different iron ore typologies. Sample analysis provides values required in the model. From the model, an alternative production plan is presented with a positive impact of USD 25.6M over the current net present value of the mining/mill system. <![CDATA[A Geostatistical Framework for Estimating Compositional Data Avoiding Bias in Back-transformation]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200219&lng=pt&nrm=iso&tlng=pt Abstract Estimation of some mineral deposits involves chemical species or a granulometric mass balance that constitute a closed constant sum (e.g., 100%). Data that add up to a constant are known as compositional data (CODA). Classical geostatistical estimation methods (e.g., kriging) are not satisfactory when CODA are used, since bias is expected when estimated mean block values are back-transformed to the original space. CODA methods use nonlinear transformations, and when the transformed data are interpolated, they cannot be returned directly to the space of the original data. If these averages are back-transformed using the inverse function, bias is generated. To avoid this bias, this article proposes geostatistical simulation of the isometric logratio ratio (ilr) transformations back-transforming point simulated values (instead of block estimations), with the averaging being postponed to the end of the process. The results show that, in addition to maintaining the mass balance and the correlations among the variables, the means (E-types) of the simulations satisfactorily reproduce the statistical characteristics of the grades without any sort of bias. A complete case study of a major bauxite deposit illustrates the methodology. <![CDATA[Performance analysis of the HRC<sup>TM</sup> HPGR in pilot plant]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200227&lng=pt&nrm=iso&tlng=pt Abstract A pilot scale test program was conducted to evaluate the size reduction performance of HPGR (High Pressure Grinding Rolls) operating in different circuit configurations. For this purpose a series of pilot-HPGR locked cycle tests were performed with medium and high pressures to simulate the HPGR operation in closed circuit with a screen, with partial product recycle, and with edge recycle. Logged instrumentation data such as roller speed, working gap, operating pressure, and power draw were used in combination with material test results such as particle size distributions, flake density, flake thickness, and bulk density of the feed for calculation of HPGR operational parameters. The paper reports the results from the pilot HPGR test work. The analysis reported herein includes an evaluation and comparison of different circuit configurations of the HPGR operation in terms of energy consumption, capacity and product fineness and also discusses the benefits of various circuit arrangements. <![CDATA[Principal environmental impacts on pipeline tracks as a result of mining operations and their mitigated actions]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672016000200233&lng=pt&nrm=iso&tlng=pt Abstract This study deals with the main environmental impacts and possible mitigation measures for many pipeline tracks, due to the mining of different substances in areas of interference between mining activities and mineral research and those resulting from construction and gas pipeline operation. By monitoring the identified interferences/disturbances, it was determined that although punctual and small in number, the extraction of mineral resources in the proximity of the gas pipelines could represent risks for the security of the undertaking. In general the risks are consequence either of the use of explosives or of induced erosive processes that could lead to pipeline instability. It is necessary to block the mining activities on both sides of the pipeline tracks in order to minimize risks to the pipeline, to others, to society, and to the environment. Also, the establishment of "flexible" track limits could be adopted in areas adjacent to the pipelines for the exploration of some mineral deposits, thus prioritizing security preservation with a minimum of socio-environmental impacts.