Resumo em Inglês:

Abstract The three-dimensional Theory of Elasticity equations lead to a complex solution for most problems in engineering. Therefore, the solutions are typically developed for reduced systems, usually symmetrical or two-dimensional. In this context, computational resources allow the reduction of these simplifications. The most recognized methods of algebraic approximation of the differential equations are the Finite Differences Method and the Finite Element Method (FEM). However, they have limitations in mesh generation and/or adaptation. As follows, Meshless Methods appear as an alternative to these options. The present work uses the Radial Point Interpolation Method (RPIM) to evaluate the stress in two-dimensional beams in regions close to loading (Saint Venant's Principle). Formulations based on the Fourier Series Theory and the RPIM are presented. Multiquadrics Radial Basis Functions were used to obtain the stiffness matrix. Two numerical examples demonstrate the validity of the RPIM for the proposed theme. The results were obtained from the formulations cited and the Finite Element Method for comparison.

Resumo em Inglês:

Abstract The geomechanical properties of rock masses must be identified to assess their quality and employability; however, the methodologies may differ depending on the lithotype and analytical purposes. The present study aimed to estimate the not-well-known physical-mechanical properties of three types of carbonate rocks (calcarenite, calcilutite, and marble) of Sete Lagoas Formation, which are not recognized in scientific literature, southeast Brazil. These are important rocks from an economic point of view, as they comprise an important input for cement, fertilizers and construction material. Both physical indexes (apparent porosity, apparently dry and saturated specific mass, apparent absorption capacity and wave propagation velocity) and mechanical properties (uniaxial compression, point load and slake durability) were determined. Mechanical tests for these three rock types were correlated to those of other carbonate rocks from other countries, for comparisons. The results showed that the lithotypes under study are peculiar in terms of porosity, wave propagation velocity and strength. Also found were a very high durability and a very good correlation between specific mass and uniaxial compressive strength.

Resumo em Inglês:

Abstract Steel and concrete floor systems are widely applied for buildings and provide excellent structural response, optimized material consumption, reduced beam height, and improved bending strength and stiffness capacity. In recent years, many experimental investigations concerned with new alternatives addressed to efficient interaction between steel and concrete structures have been reported. In this context, the present study aims at investigating the behavior of a structural composite floor system composed of light cold-formed steel trusses and a partially pre-cast concrete slab, as well as developing an innovative solution for shear connectors. The referred to shear connector consists of Thin-Walled Perfobond (TWP) ribs, composed of 1.25mm thick cold-formed plates crossed by 4.2 mm reinforcing steel bars and connected to the truss chord by self-drilling screws. Preliminary results, based on experimental full-scale testing, indicate that the performance of the composite truss is adequate in terms of ultimate load and deformation capacity. Additionally, the investigation showed that traditional analytical solution is in good agreement with experimental results.

Resumo em Inglês:

Abstract The present article proposes to apply a Risk-Based Maintenance methodology in a gas compression system. This risk calculation is based on a semi-quantitative mathematical model that uses the interdependence of process variables and predictive maintenance data applied in a Condition-Based Maintenance methodology, in order to obtain the calculation of the dynamic risk. This promotes a review of maintenance and reliability strategies proactively in real time. The dynamic risk applied to the system involves the interface of predictive maintenance and process variables with the reliability and risk analyses of the system. This value, which is associated with the financial aspects, safety, people and environment, can be compared to the tolerable risk of production plant operation, providing operation or maintenance decisions. An example demonstrates the integration of process and maintenance data using this model methodology for a gas compression system. This framework can be applied to evaluate the integrity of systems, providing critical risk-based information for the maintenance and operation teams, assisting then in the mitigation of failures in the production systems.

Resumo em Inglês:

Abstract This study presents an optimization method for the thickness of shell elements subjected to dynamic loads. Structural analyses were carried out using the finite element method. The analyzed domains were modeled using NURBS, and meshes were generated using a transformation of the parametric domain into the geometric domain via a geometric function. The shell element considered is a combination of a CST membrane element and a DKT plate element, forming an element with 15 degrees of freedom. The Newmark method with constant acceleration was applied to solve the equation of motion. The optimization approach was considered in two different ways: with uniform and variable thickness throughout the shell element. Due to the nonlinear constraints of the problem, the Sequential Quadratic Programming (SQP) method was employed. SQP routines are available in MATLAB, in which this study was performed. Useful examples were detailed in this study to demonstrate the applicability of the optimization method to real structures, such as the Igrejinha da Pampulha, a church located in Belo Horizonte, Brazil, whose modeling was performed.

Resumo em Inglês:

Abstract The study identifies the Canastra-3 Kimberlite magnetic anomaly as the likely primary source of the alluvial diamonds recovered by "garimpeiros" in the Santo Antônio River basin (Delfinópolis, southwestern Minas Gerais). This conclusion is based on cumulative geophysical, hydrographic, metallogenical and mineral geochemistry evidences. The study area is located within fertile ground in the border of the São Francisco craton, close to other diamond primary sources and secondary deposits. This kimberlitic target is the only known in the Santo Antônio River basin. In addition, the known mineralized gravels of this river, worked in the past by "garimpeiros", have evidence of a short transport (angular pebbles and blocks), further evidence of a nearby source. The original data collected in the "Minas Gerais Aerogeophysical Survey Program" was processed and analyzed with the Euler Deconvolution method, implemented in software Oasis Montaj. With the exception of the Canastra-3 body anomaly, all others in the study were classified as non-kimberlitic. Recent sampling work on the weathered top of the Canastra-3 Kimberlite recovered indicator minerals, notably a high proportion of pyrope garnets of the G-10 type, which is unusual among the kimberlites of the region.

Resumo em Inglês:

Abstract Obtaining rare earth elements (REE) is a complicated task, due mainly to the difficulty of separating and purifying them. Solvent extraction is the most widely used technique for separating REE, and the most common extractants used are organophosphorus acids. The low selectivity of this technique leads to the need for a high number of extraction cells. To increase the selectivity and separation and avoid the practice of saponification of the extractant, the use of complexing agents has been studied, such as low-molecular-weight and biodegradable weak organic acids. The objective of this research was to study the separation of the rare earth elements Gd and Eu by the solvent extraction technique using the organophosphonic extractant 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507). Assays were performed using non-saponified and saponified P507 extractant and adding lactic acid to the aqueous phase prior to extraction. Experimental factorial planning was used to study the effect on the extraction and separation of the Eu and Gd of the variables extractant concentration, initial feed pH, saponification degree, and lactic acid concentration. The greatest Gd extractions were obtained when lactic acid was added to the feed solution. Also, saponification of the extractant and lactic acid addition improved the Gd/Eu separation. The number of stages required to extract Gd using McCabe-Thiele diagrams was estimated, whether or not the solution was conditioned with lactic acid. The largest extraction percentage was obtained by adding lactic acid in a continuous counter-current extraction assay, achieving 94% Gd extraction.

Resumo em Inglês:

Abstract The importance of the Santa Gertrudes Ceramic Complex (SGCC) in the ceramic market is directly associated with the high quality of the Corumbataí Formation clays used in the manufacture of its products. Although the volumetric capacity of the Corumbataí Formation is able to meet the SGCC demand for the coming years, its industries are always in search of alternative sources for raw material, among these sources is the Tatuí Formation. In order to determine if the sediments coming from the Tatuí Formation have the potential to be used in the ceramist industry, geochemical, mineralogical and physical characterization tests were carried out on samples obtained from two different profiles. The analyses showed a sequence of fine sandstones rich in SiO2 and Al2O3, with a mineralogy composed of quartz, potassium feldspar / plagioclase (albite), filosilicates and iron oxides in secondary proportions. The ceramic tests, in turn, presented heterogeneous results for the specimens submitted to burning at 1150 º C, but in general, the material coming from the Tatuí Formation has a promising potential within the field of ceramic manufacturing.

Resumo em Inglês:

Abstract The effect of titanium and nitrogen addition on Hadfield steels was investigated. In order to do this, two grades of steels were produced in terms of titanium and nitrogen addition. The final samples had their microstructure characterized and their mechanical properties were evaluated by uniaxial tensile and Charpy impact tests. Furthermore, the wear resistance was measured by dry sand rubber wheel abrasive tests. Microscopy analyses demonstrated that the precipitation of titanium carbonitrides resulted in a coarse microstructure, with large columnar grains coexisting with equiaxed ones. Consequently, these samples presented lower mechanical properties in comparison with the samples without titanium and nitrogen, which showed a finer microstructure. On the other hand, the presence of hard Ti(C, N) precipitates in the microstructure improved the abrasive wear performance of the steel during the abrasive tests.

Resumo em Inglês:

Abstract Phytomining is suggested as a technology to obtain platinum group metals (PGMs) nanoparticles from plants grown on the mineralized soils or tailings. Samples from North American Palladium (Canada) and gossans from Broken Hill (BH) (Australia) were studied to assess the possibility of using these PGM-rich samples as substrates for phytomining. The bioavailability of PGMs was indirectly assessed using geochemical procedures. The selective extractions showed that the highest available concentration of Pd is 5.38 ppm in BH gossan 1. The extraction of PGMs by ammonium acetate, fulvic acid or citrate-dithionite indicates natural availability to plants. The BH gossan 1 was the best of the five studied samples for phytomining of Pd due to available Pd concentration (> 2 mg/kg), low Electric Conductivity (< 2dS/m), high CEC (Cation Exchange Capacity) (38.8 meq/100g), and proper pH (6.5). Cu-tolerant plant species should be chosen to grow on BH gossan 1. A criterium for choosing substrates for phytomining of Pd was developed comprising various classical soil parameters plus selective extraction procedures.

Resumo em Inglês:

Abstract The current economic and political scenario in Brazil has allowed small, medium and large companies to adopt cost cutdown and productivity increase strategies. Diesel fuel consumption by off-highway haul trucks stands for one of the largest costs at the Sossego Mine operational management department. Based on this fact, as well as on the 8% increase in the budgeted diesel fuel cost for 2017, the mining unit has decided to implement a project, previously implemented at the Capão Xavier mine site, which makes use of a high-fidelity haul truck simulator for operators' qualification, by working on the major factors impacting fuel consumption. The application of the simulator has been observed to be a potential upturn for the identification and correction of major failures and bad habits impacting fuel consumption. The results suggest a significant diesel fuel consumption cutdown, as well as enhanced haul truck operation ability and performance.

Resumo em Inglês:

Abstract Ferricyanide Fe(CN) 6 3- is one of the most stable cyanometallic complexes present in the gold mining effluents. This cyanocomplex is hard to degrade by natural attenuation and generates a negative impact on aquatic environments. Although free cyanide (CN-) can be obtained by acidifying the solution, the CN- is lethal for all forms of life. The oxidation of Fe(CN) 6 3- in a typical photocatalitic system was evaluated with the addition of H2O2. To verify the degradation, chemical parameters, such as free cyanide, the formation of ammonia, nitrate, and total iron were analyzed at the end of the process. Different parameters were evaluated to analyze the behavior of the degradation: 1. dark stage adsorption using the catalyst, 2. the TiO2 dosage, 3. Addition of H2O2, 4. UV radiation power (120 and 200W) and finally a test of TiO2 with solar radiation. The photolysis effect from a ferricyanide solution at 100 mg L-1 at alkaline pH 13, showed that the complex studied is highly stable since under UV irradiation conditions (l> 300 nm), a low rate of dissociation was observed. After 24h of irradiation, the cyanocomplex was under 20%, whereas degradations up to 70% were obtained in a heterogeneous photocatalysis system with TiO2. The best result was achieved with the H2O2 and TiO2 photocatalytic system, and the stoichiometric concentration was about 2.5 times less than the peroxide used in the gold mining industry, reaching 83% degradation. The photocatalytic process obtained less toxic byproducts than the original synthetic ferricyanide used as mining wastewater.

Resumo em Inglês:

Abstract Mining is very important to the economic, political and social development of the Minas Gerais State in Brazil ever since the time the country became a Portuguese colony in the early 1500s. However, few researches have been conducted to evaluate the environmental impacts associated with the mining activity at this time. There are many abandoned mines in Minas Gerais; these are mainly gold mines inherited from the colonial period, which have been considered to represent a considerable environmental liability. However, when a road was constructed in a rural area of the municipality of Descoberto, Minas Gerais, in 2002, a significant amount of mercury was detected in an abandoned gold mine. In 2014, the State Public Prosecutor's Office found both the State of Minas Gerais and the State Environmental Agency liable and responsible for this occurrence and ordered them to design an intervention project for the contaminated area that involved mine closure. This article provides information on how mercury contamination occurred and estimates the amount of mercury present in the contaminated area, with the aim of supporting proposals of alternative remediation, monitoring and management therein. This study includes a historical survey of mining operations in the region and a brief history of the use of mercury in amalgamation. Estimations are made of the amount of gold produced and the amount of mercury released into the environment between 1850 and 1892. Results show an estimated mass of 820 kg of mercury contained in soils and sediments within an area smaller than 1 hectare.

Resumo em Inglês:

Abstract The traditionally and widely used Lerchs-Grossmann algorithm presents well-known limitations that newer propositions attempt to overcome. The direct block schedule (DBS) methodology, which has gained relevance with computational advances, obtains the final pit as a natural result of production sequencing, different from Lerchs-Grossmann-based algorithms. This process flow applies constraints in the final pit definition stage attempting to provide a more realistic result and to minimize risks. Slope instability is a common and inherent risk to open pit mining and may affect the project's net present value (NPV). A study of the impacts of slope angle variations on safety indexes and final pit NPV provides an auxiliary tool for the overall slope angle definition process. This article presents a case study in which the effects of variations of the overall slope angle on the safety factor (SF) and project NPV were analyzed. A total of 25 pits were generated by each studied final pit definition methodology, and each pit had the sections with the varied slope angles analyzed in the stability assessment, resulting in a total of 150 slopes analyzed. A comparison between the results obtained by the two different methodologies implemented in commercial software is presented. The results show no relationship between the NPV and the overall slope angle using the DBS methodology. An analysis of the results for each geotechnical sector obtained by the traditional methodology was conducted and may contribute to the trade-off analysis between the best slope angle to achieve a reasonable SF and the maximum NPV.

Resumo em Inglês:

Abstract The inefficiency in controlling the slurry/froth interface level of a scavenger column flotation stage was severely impairing the process performance of an iron mining company, increasing the iron content in the tailings to levels above 20% and, consequently, not meeting the company's iron recovery and pellet feed production targets. Based on mass balance and process data, hydraulic calculations were performed and showed that the installed 6.0" (15.24cm) diameter barometric leg tubes and the control system valve were adequate. An equation to determine the maximum barometric leg height was developed for the flotation column and other calculations showed the necessity to reduce this height from 4.6m to a maximum of 3.4m. The barometric leg adequacy considerably decreased the variability in controlling the slurry/froth interface level, reduced the iron content in the tailings from 24.9% to 18.9% and increased the iron recovery in the flotation stage from 97.9% to 98.7%.