Resumo em Inglês:

Abstract Tunnel boring machines are important tools in underground infrastructure projects. Although being well established equipment, these machinesare based on designsof more than 60 years ago and are characterized by big dimensions, enormous weight and high power consumption. Commercial aspects should be noted too. The model adopted by the TBM industry requires constant replacement of cutter discs and specific labor skills, usually offered by the same manufacturingcompany. In some cases the cost of replacement parts and technical assistance can be higher than the acquisition cost of an entire machine. These aspects are no longer compatible with the concept of sustainability that is an important aspect of currentsociety. While the technical characteristics require a large quantity of steel and several inputs, the adoptedmodel is not competitive. One alternative is looking for new technologies that break the old paradigms and allow the development of high performance concepts with lower social and environmental impact. This studydealswith this opportunity by proposing a high performance tunnel boring machine that makes use of high power water jet and diamond wire to compose a double shield cutter head. It works in two stages. In the fristone, an annular cut is executed by hydrodemolition,and in the second one, the diamond wire station slices the rock core. Only with the action of diamond wire is the rock core separated from the rock mass and the removal process is finished. A smart water jet nozzle movement system is described and non circular tunnels can be executed. The new technologies involved requirea different type of backup system, lighter and smaller. The non-existence of mechanical contact between the equipment and the rock mass at theexcavation front allows low power consumption. The advanced rate and primary excavation cost analyses can also be encountered herein. It shows that it is possible to reach an advanced rate of 174 m/day in soft and porous rock and 0.64 m/day in hard and non porousrock, whereas the NTNU method indicates only 55m/day and 13m/day underrespective conditions. On the other hand, the excavation cost is high for both conditions. One option is to use sand as an abrasive in the water jet process, reducing by half the primary excavation cost. It is reasonable to say that the proposed concept can be considered as an alternative for tunnels in soft rock and high porosity, and needs better performance of the water jet system to become an alternative for hard rock.

Resumo em Inglês:

Abstract The Petrolina County, Pernambuco State, Brazil, presents specificities that make it unique from a hydrogeological point of view. Water resource scarcity is both a quantitative and qualitative issue. The climate is classified as semiarid, having low precipitation, along with high temperatures and evapotranspiration rates. Aquifer zones are related to low connected fractures resulting in a restricted water flow in the aquifer. The recharge is limited and the groundwater salinity is high. Stable isotope analyses of H and O were developed in groundwater samples (with different electrical conductivity) and surface water collected in a bypass channel flowing from the São Francisco River. The results were plotted in a dD ‰ versus δ18O ‰ graph along with the curves of the global and local meteoric water line. Groundwater samples showed unexpected results showing a lighter sign pattern when compared to the meteoric waters. More negative dD and δ18O values indicate an enrichment in light isotopes, which show that this process is not influenced by surface processes, where the enrichment occurs in heavy isotopes due to evaporation. The isotopic signature observed is interpreted either as resulting from the water-rock interaction, or as resulting from recharge from paleo rains. The waters are old and show restricted flow. So the water-rock contact time is extended. In the rock weathering processes, through the hydration of feldspars, there is preferential assimilation of heavy isotopes at the expense of the lighter ones that remain in the water. Analyses of the 87Sr/86Sr ratio and isotopic groundwater dating assist in the interpretations.

Resumo em Inglês:

Abstract The Chapada Diamantina, located in the central region of the State of Bahia, is of important historical significance due to its diamond occurrences. Discovered in the nineteenth century, comprehensive research about the regional diamonds and their origins are still limited, demanding more investigation in the matter. Looking for insights about their genesis, mineral inclusions in 23 alluvial diamonds from 4 garimpos located in the Chapada Diamantina were analyzed through the use of Raman micro spectroscopy. Additionally, the characteristics of nitrogen aggregation of the host diamonds were measured using Fourier-transform infrared spectroscopy (FTIR). The diamonds from Chapada Diamantina consist mainly of well-formed crystals, with dominant dodecahedral habits, characterized by faint to very light yellow body colors, typically with green and brown radiation spots on their surface. The main surface textures observed are related to processes that took place in the late stage resorption and during the residence of the diamonds in placer environments. The diamonds are predominantly type IaAB, with a significant occurrence of poorly aggregated nitrogen (Type IaA diamond). The main mineral assemblages of the studied peridotitic inclusions refer to a harzburgitic paragenesis.

Resumo em Inglês:

Abstract The Espinhaço Range, in the Diamantina region (central part of the State of Minas Gerais), is known worldwide as a famous source of associated occurrence of quartz, rutile and/or anatase crystals. The latter is also a classic accompanying mineral of diamonds in the alluvial placers. Primary anatase is related to hydrothermal quartz veins cutting geological units of the Espinhaço Range. In the last decade, outstanding large sized anatase crystals (up to 4 cm) in such veins have been reported from two areas, showing unusual habits and partial intergrowth with rutile. They are colorless, ocher brown, or golden yellowish, often double terminated, and iron rich. Due to their strong adamantine luster and pseudo-octahedral habit, some resemble diamonds. Two different morphological types have been studied: a simple crystal habit solely with {011} faces, and double terminated complex anatase crystals with one or more of the following forms: {011}, {012}, {013}, {017} and {112}. The geological environments as well as general mineralogical characteristics are also described.

Resumo em Inglês:

Abstract We applied a method of Simultaneous Prestack Seismic Inversion (SPSI) in a hydrocarbon field located in the Campos Basin, Brazil. The goal was to study the application of this method to Albian carbonate rocks of the Quissamã Formation. Based on what is found in nearby fields, this Formation potentially contains hydrocarbon accumulations that can be revealed with the inverted models. P-wave velocity (Vp), S-wave velocity (Vs) and density (ρ) curves along seven wells were used as inputs to construct 3-D initial models of acoustic impedance (Zp), shear impedance (Zs) and ρ. Wells without Vs and ρ curves had those values calculated from well-established equations. Final 3-D models were calculated from deviations in linear relationships between the logarithms of Zs and Zp, as well as between ρ and Zp, which were merged with the initial models. Interpretations of the inversion results were conducted based on patterns found along well logs such as resistivity (ILD), gamma ray (GR), density (RHOB), neutron porosity (NPHI) and sonic (DT). These analyses provided criteria to select the best inverted models. These models show low impedance anomalies that are consistent with previous studies performed with the well logs. One well in particular was interpreted as having high potential to contain hydrocarbons. This well shows an impedance pattern that allowed us to highlight other areas with the same pattern throughout the entire seismic volume.

Resumo em Inglês:

Abstract Metal droplets generated by an impinging jet, play an important role in metal refining processes, mainly in oxygen steelmaking, where the droplets are ejected into the slag phase. Since the available interfacial area of droplets is very high in this process, the generated droplets enhance the rates of heat transfer and chemical reactions. Therefore, knowledge of the metal droplet generation rate, size distribution and residence time in the slag are of industrial relevance. In this work, the isothermal, transient flow of an incompressible air jet impinging onto an air/water interface at room temperature has been simulated to obtain a better understanding of the droplet ejection phenomenon. The interface was tracked throughout time using the volume of fluid (VOF) technique. The governing equations formulated for mass and momentum conservation and the k-e turbulence model are solved in the axisymmetric computational domain using the commercial code FLUENT. The droplet ejection rates calculated with computational fluid dynamics model are compared to experimental data reported in literature, showing partial agreement, being the incompressibility assumption the probable reason for the deviation observed, which was as far pronounced as the great jet velocity. Nevertheless, the model presented shows itself as a relatively good starting point for the construction of more complex ones (with less simplifying assumptions) which should be able to offer a means to increase the understanding of the droplet ejection phenomena.

Resumo em Inglês:

Abstract This study aims to analyze the efficiency of niobium and vanadium carbides in the high energy mechanical milling of aluminum bronze alloy. Two series of experiments were made following the same steps for both niobium carbide (NbC) and vanadium carbide (VC) additions: 30 g of chips were weighed and placed in a stainless steel jar with 3 % of carbide and 1 % of stearic acid for a mass/sphere relationship of 1:10. The milling was realized using a planetary ball mill for 10, 30 and 50 hours in an inert argon atmosphere at 300 rpm. Results shown in laser diffraction indicate a great reduction in the particle sizes of powders when VC is used. For 30 hours milling, D50 values ranged from 1580 µm with NbC to 182.3 µm with VC addition. The D50 values ranged from 251.5 µm with NbC to 52.26 µm with VC addition, for 50 hours milling. The scanning electron microscopy showed that in 10 hours of milling, the energy was not sufficient to achieve the shear of chips in both cases. For 30 hours, it's possible to observe particles with sizes between 100 µm and 800 µm with NbC addition while for the same milling time, with VC it's possible to see particles with different sizes, but with many shapes of fine particulates. For 50 hours milling, particles achieved the smaller sizes between 50 and 200 µm with NbC and ranging from 5 until 50 µm with VC addition.

Resumo em Inglês:

Abstract Production cost reduction for the Electric Arc Furnace (EAF) technology is strongly dependent on the efficiency of the electrical energy being introduced into the metal bath. Besides EAF technology, the slag foaming process is currently applied to some other equipment for steel production aiming to save energy, productivity improvements, enhance the refractory service life and inhibit steel re-oxidation. In this way, this study involved the recycling options of Crushed MgO-C spent refractories removed from the EAF without complex and costly beneficiation, with emphasis on its application as a slag conditioner, since its composition presents high MgO content. The experiments were performed in a laboratory induction furnace and the temperature was controlled at 1700°C.The initial height of the slag was recorded and foaming briquettes added into the furnace. The experiments were carried out for 30 minutes. When the foaming process was finalized, an aliquot from the slag was collected to be analyzed by chemical analysis. Then, the metal with slag was tapped into a mold. The results indicated that the best viscosity was 0.39poise. The maximum height of foam formation was observed for a binary basicity greater than 1.2. The concentration of MgO in the slag is close to the saturation point.

Resumo em Inglês:

Abstract One of the characteristics of Civil Construction is its ability to absorb a wide range of wastes to produce new products. Therefore, the objective of this study was to evaluate the behavior of cement plates produced with the addition of ground glass wool waste and in natura, in shredded form. The tensile strength tests in bending and permeability were performed, according to ABNT NBR 15498: 2007 as well as environmental ones according to ABNT NBR 10004: 2004. The plates produced in this study were characterized as being impermeable, with a satisfactory tensile strength in bending and being classified as plates for indoor and outdoor use, and as products that do not offer immediate risk to health and to the environment; however, it should be discarded in landfill.

Resumo em Inglês:

Abstract A numerical model based on transport equations for momentum, energy and chemical species for the gas and solid phases is proposed to simulate the inner phenomena in the direct reduction of the shaft furnace process for producing directly reduced iron (DRI). The model is verified using industrial data for productivity, raw materials and final composition of the DRI product. The model is used to evaluate operational practices using new raw materials and the composition of the reducing gas in the process. Three cases were considered, which correspond to available raw materials commercialized by different suppliers. The effects on the gas and solid inner temperatures, pressure and phase composition distributions are quantified. The simulation results indicated that good agreement for overall parameters of the process could be achieved and afterwards, detailed features of the inner conditions of the process are predicted.

Resumo em Inglês:

Abstract Blasting remains as an economical and reliable excavation technique, but there are some environmental shortcomings such as the control of blast-induced vibration. The impacts of vibration over surrounding communities in a blast area have been investigated for decades and researchers have been using a myriad of empirical predictive attenuation equations. These models, however, may not have satisfactory accuracy, since parameters associated to geomechanical properties and geology affect the propagation of seismic waves, making vibration modeling a complex process. This study aims for application of an Artificial Neural Network (ANN) method and Geomechanical parameter relationships to simulate the blast-induced vibration for a Brazilian mining site and then compare them to the traditional approach. ANN had the best performance for this mine despite having demanded large datasets (as much as for the traditional approach), while geomechanical parameters like RQD and GSI may be used to deliver a fair approach even without seismic data. Also, ANN methods may be useful in dealing with a large amount of information to facilitate the simulation process when combined with other methods. Therefore, alternative prediction methods may be helpful for small budget mining operations in planning and controlling blast-induced vibration and helping mining in urban areas becoming a more sustainable activity.

Resumo em Inglês:

Abstract This study is focused on Direct Block Scheduling testing (Direct Multi-Period Scheduling methodology) which schedules mine production considering the correct discount factor of each mining block, resulting in the final pit. Each block is analyzed individually in order to define the best target period. This methodology presents an improvement of the classical methodology derived from Lerchs-Grossmann's initial proposition improved by Whittle. This paper presents the differences between these methodologies, specially focused on the algorithms' avidity. Avidity is classically defined by the voracious search algorithms, whereupon some of the most famous greedy algorithms are Branch and Bound, Brutal Force and Randomized. Strategies based on heuristics can accentuate the voracity of the optimizer system. The applied algorithm use simulated annealing combined with Tabu Search. The most avid algorithm can select the most profitable blocks in early periods, leading to higher present value in the first periods of mine operation. The application of discount factors to blocks on the Lerchs-Grossmann's final pit has an accentuated effect with time, and this effect may make blocks scheduled for the end of the mine life unfeasible, representing a trend to a decrease in reported reserves.

Resumo em Inglês:

Abstract Niobium metallurgical recovery measures how much of the metal content in the ore is separated in the concentrate after the mineral processing stages. This information can be obtained through laboratory tests with ore samples obtained during drilling. Thereunto, representative ore samples are subjected to tests mimicking the ore concentration processing flow, but these experiments are time consuming and costly. The main objective of this study was to develop a more efficient way to obtain the metallurgical recovery information from ore samples. Based on the development of chemometrical studies, the chemical components currently analyzed in the ore with correlation to the metallurgical recovery were identified. These correlated variables were used to build a nonlinear multivariate regression model to explain the response variable, i.e. metallurgical recovery. The Principal Component Analysis was used in this work to define which chemical variables contribute most to explain the metallurgical recovery phenomenon. The Second order regression equation (Response Surface) was the most suitable methodology to explain the metallurgical niobium recovery and was created by the interaction of the five most important chemical variables. After the exclusion of outliers, the linear regression coefficient between the metallurgical recovery calculated and the metallurgical recovery analyzed was 82.59%. The use of the second order regression equation contributes to reduce the amount of experimental analysis to assess the geometallurgical niobium ore response, promoting the reduction of costs for metallurgical characterization of the ore samples. The methodology proposed proved to be efficient, maintaining an adequate precision in the forecasted response.

Resumo em Inglês:

Abstract The use of a gouging abrasion test to evaluate the wear of jaw crushers is revised in terms of its procedures, considering the effects of the most significant variables, such as the minimum amount of crushed material and the minimum opening between the jaws during the crushing cycle (minimum discharge aperture). A correlation between the work hardening of jaws and the amount of crushed material is presented. The wear of stationary and movable jaws is compared, being the results dependent on the jaw's material and the discharge aperture. The abrasiveness of several rocks was evaluated, showing a good correlation with their Mohs hardness.

Resumo em Inglês:

Abstract Short-term mining planning typically relies on samples obtained from channels or less-accurate sampling methods. The results may include larger sampling errors than those derived from diamond drill hole core samples. The aim of this paper is to evaluate the impact of the sampling error on grade estimation and propose a method of correcting the imprecision and bias in the soft data. In addition, this paper evaluates the benefits of using soft data in mining planning. These concepts are illustrated via a gold mine case study, where two different data types are presented. The study used Au grades collected via diamond drilling (hard data) and channels (soft data). Four methodologies were considered for estimation of the Au grades of each block to be mined: ordinary kriging with hard and soft data pooled without considering differences in data quality; ordinary kriging with only hard data; standardized ordinary kriging with pooled hard and soft data; and standardized, ordinary cokriging. The results show that even biased samples collected using poor sampling protocols improve the estimates more than a limited number of precise and unbiased samples. A welldesigned estimation method corrects the biases embedded in the samples, mitigating their propagation to the block model.

Resumo em Inglês:

Abstract The presence of slimes is harmful to the flotation process: the performance and consumption of reagents are negatively affected. Traditionally, the desliming stage has been responsible for removing slimes. However, depending on the porosity of the mineral particles, desliming may not be sufficient to maximize the concentration results. An attrition process before the desliming operation can improve the removal of slime, especially when slimes cover the surface and/or are confined to the cavities/pores of the mineral particles. Attrition is present in the flowcharts of the beneficiation process of phosphate and industrial sand (silica sand). Research has been undertaken for its application to produce pre-concentrates of zircon and iron ore. However, there is still little knowledge of the influence of the attrition variables on the beneficiation process of iron ore. This study presents a factorial design and analysis of the effects of these variables on the reverse flotation of iron ore. The standard of the experimental procedures for all tests included the attrition of pulp, under the conditions of dispersion, desliming and flotation. The parameter analysed (variable response) was the metallurgical recovery in reverse flotation tests. The planning and analysis of the full factorial experiment indicated that with 95% reliability, the rotation speed of the attrition cell impeller was the main variable in the attrition process of the iron ore. The percentage of solid variables in the pulp and the time of the attrition, as well as their interactions, were not indicated to be significant.