Resumo em Inglês:

Abstract It is well known that learning about the mechanical behavior of a fractured rock mass depends on the shear behavior of its discontinuities. Several studies have shown that the shear behavior of unfilled rock discontinuities depends on their boundary conditions, roughness characteristics and the properties of the joints walls. Currently, there are several analytical models that can be used to predict the shear behavior of clean rock joints. However, they are all purely deterministic in nature because their input variables are defined without considering the uncertainties inherent in the formative process of the rock mass and the discontinuity itself, i.e., they need an auxiliary tool to consider the variability of their parameters such as the Monte Carlo or Point Estimation Methods. Therefore, the purpose of this article is to present a model to predict the shear strength of clean rock joints incorporating uncertainties in the variables that govern their shear behavior with a zero-order Takagi-Sugeno fuzzy controller. The model is developed based on the results of 44 direct shear tests carried out on different joints. The model input variables are the normal boundary stiffness and initial normal stress acting on the joint, its roughness expressed by the JRC value, the uniaxial compressive strength and basic friction angle of the intact rock, as well as the shear displacement imposed on the joint. The results showed that the predicted shear strength of clean rock joints obtained by the fuzzy model fit the experimental data satisfactorily and helped define the shear behavior of the discontinuity.

Resumo em Inglês:

Abstract Recent scientific and computational advances have facilitated the analysis of slender structural systems subject to instability. With the employment of more sophisticated numerical tools and algorithms, it is possible to accurately determine the critical points (limit and bifurcation loads) as well as the post-critical behavior of the structural system. In the computational context, efficient data structures are needed to enable code and graphic interface expansion for the generation of models and visualization of the results obtained. Thus, an interactive object-orientated graphic computational system is presented herein. It has been developed using MATLAB/GUI, with pre-processing, analysis and post-processing capacities for planar structural frames. The nonlinear finite element developed and implemented for the structure modeling is formulated considering second order effects. Therefore, with the computational tool presented, the geometric nonlinear effects and stability of the structural system can be directly addressed, and the visualization of the numerical results are accessed through interactive controls that permit data inclusion and analysis verification. The engineer-designer can see the structural model discretization, the equilibrium path, its deformation configuration, the force and bending moment diagrams at the moment that he runs the program and in each load step. It is also possible to export the images, videos or tables of the obtained numerical results. The example presented demonstrates the capacity of the developed graphic computational system.

Resumo em Inglês:

Abstract The problem of symmetric cross-section beams under oblique bending is well known to professional designers and academy. In fact, symmetric elements make up most of the cross-sections defined in design. The case of the asymmetric cross-sections is, however, little discussed in literature, but is a particular problem, especially in bridge girder design, joined in loco. The asymmetry generates oblique bending when the load is out of the principal inertia planes. Thus, this article presents a comparison of results between a numerical solution of the elastic curve differential equations, and a Finite Element Model (FEM), for a 10m span reinforced concrete beam, with gutter-shaped asymmetric cross-section, whose only load is its own weight. The required geometric properties were determined by the Green Theorem. From theoretical study, the elastic curve differential equations were obtained, in the vertical and horizontal directions. The angular displacement conditions at the beginning of the span were obtained by the Virtual Work Method. After integration using the Runge-Kutta Method, the maximum displacements in the vertical and horizontal directions, in the middle span, are 0.904cm and 0.611cm, respectively (1.091cm resultant displacement). The Finite Element Model was performed in ANSYS 9.0. The resultant displacement of the numerical model was 1.16cm. Concurrently, the axial stresses were studied in the middle span. The stress results for both approaches (Runge-Kutta and FEM) differed by no more than 8.72%. These results guarantee reliability to the Runge-Kutta integration, from a design view point, to the proposed problem analysis in Serviceability Limit State.

Resumo em Inglês:

Abstract Caves hosted in iron formations are attracting considerable interest due to their scientific and environmental value. Some of these caves are located in or near iron ore mine sites, which represent an important source of income to Brazil. However, the Brazilian legislation requires speleological studies that currently have an impact upon ore reserves and environmental licensing processes. The aim of this study was to apply conventional geotechnical empirical approaches to a cave located within the grounds of an iron ore mine in the Iron Quadrangle and validate it with numerical modelling, to ensure the method's applicability to natural caves under mining activity influence. These studies comprised the mapping of structural, geotechnical and geomechanical features of rocks hosting and surrounding the cave and to propose geotechnical domains. Field data collection covered the geotechnical parameters necessary to calculate the characteristic Mining Rock Mass Rating (MRMR) for each geotechnical domain, and to evaluate the stability conditions using the stability index or hydraulic radius of the cave. These geotechnical parameters were then used to calculate the physical parameters used in two-dimensional numerical simulations to verify the good stability conditions of the cave, corroborating the adequacy of Laubscher's diagram. The results of this study, although comprising only one cave, suggest that Laubscher's diagram is applicable for assessing the geotechnical behavior of iron ore caves.

Resumo em Inglês:

Abstract High transformation temperature shape-memory alloys (HTSMA) usually present a martensitic transformation temperature (Ms) starting at 100 ºC. That is the case of high nickel Ni-Ti-Hf alloys. This article presents experimental results obtained from arc melting of Ni50Ti50-XHfX .at% (X = 8, 11, 14, 17 and 20 .at%) alloys. This process homogenized every composition with similar relative crystallinity. Results confirm that transformation temperatures (TT) increase with increasing the amount of Hf. A martensitic matrix is formed by two metastable phases: R and B19'. From all the alloys studied, the B19' phase presented the highest percent fraction. Gradually adding Hf3 .at% promoted a slow increase of crystalline fraction of R phase and a slow reduction of phase (Ti, Hf)2 Ni, located at grain boundaries. Coherent/semi-coherent interface between (Ti, Hf)2 Ni phase and the matrix may intensify the driving force for the formation of R phase, present on X-ray diffractograms.

Resumo em Inglês:

Abstract Coal blend bulk density is an important property in the coking process. Some variables, such as moisture and particle size, which are controlled or measured in the coal beneficiation process in steel mills, exert a strong influence on this feature. This study aims to understand the density variation of coal blends by the influence of moisture and particle size when using dry and wet bases. The investigations showed that higher density can be reached when drying the coal blend or even with excess of moisture by an agglomeration process. However, for a coal blend of lower moisture content, such as 4%, the better effects on the coking process are evident. Changes on the density from particle size require care, since they can fall in a region of high density achieved by larger particles or in a region with excess coal fines, where either or both can compromise the coke quality.

Resumo em Inglês:

Abstract The rheological behavior of poly (butylene adipate-co-terephthalate) (PBAT) and its composites prepared with three different organoclays was investigated. Composites containing up to 7.5%, w/w organoclay, were prepared by two routes: (a) direct melt blending in an internal laboratory mixer with high intensity rotors and (b) concentrates (prepared in the internal mixer) with 50 %, by weight, of the organoclays diluted in a co-rotating twin screw extruder equipped with a high intensity mixing thread operating at a nominal speed of 480 rpm. The samples were characterized by both torque and parallel plate rheometry. Results indicate that nanodispersions in the clay layers were obtained during processing and that, like the pure matrix, at high shear rates, the organoclay compounds follow the power law, although with higher viscosity. It is believed that the interaction of the polymer with the organoclay is responsible for the increase in melt viscosity (observed by increases in torque and relaxation time) of the hybrid systems.

Resumo em Inglês:

Abstract The Brazilian ferroalloy industry faces a highly competitive scenario in the foreign market. Among the key factors to determine the price of its products, electric energy stands out as one of the main inputs. So, the possibility of energy being unavailable or having high prices causes a direct impact in the ferroalloy chain. On the other hand, the renewable energy market, especially the solar photovoltaic (SPV) energy shows extensive growth due to technological advances and recent regulation. Connecting both contexts, this study investigates a way to apply the great moment of the SPV energy sector to the ferroalloys industry. Firstly, the ferroalloy sector data was searched in order to develop a model of ferroalloy production by using the average data of production and electric energy consumption, called model-ferroalloy. So an SPV power plant was estimated to supply its electric energy demand. It was considered in four different scenarios according to current law and its economic viability verified. From these studies, the viability of implementing solar photovoltaic energy to ferroalloys industry was determined. The levelized cost of energy (LCOE) comparative shows that SPV energy has a lower price than conventional sources, no matter if it is in the free or regulated energy market. Furthermore, the necessary investment, according to the results found, has good attractiveness in the financial market point of view.

Resumo em Inglês:

Abstract In the Conceição - MG mine, there are significant reserves of dolomitic itabirite, which is considered overburden material. This study aimed to develop a flotation route for the concentration of this dolomitic BIF according to the requirements of the steel industry. The characterization of samples, comminution, liberation size, microflotation of the pure dolomite and hematite minerals were performed to establish the conditions for selective separation in bench flotation tests. The microflotation tests showed that the soybean oil at pH 6 preferably floats the dolomite in relation to the hematite. The corn starch depressant at a pH higher than10 preferably depresses the hematite relative to the dolomite. The bench flotation tests revealed interactions between the factors pH, percentage of solids in the pulp, soybean oil and starch dosage. The optimal results for bench flotation tests were achieved under the following conditions: pH at 10.5, percentage of solids of 27wt%, dosages of soybean oil and corn starch of 400g/ton and 351g/ton, respectively.

Resumo em Inglês:

Abstract This article presents a numerical model based on the finite difference method for the physical and geometric non-linear analysis of a one-dimensional consolidation problem regarding a saturated, homogeneous and isotropic soil layer with low permeability and high compressibility. The problem is formulated by adopting the void ratio as the primary variable, considering a Lagrangian movement description. The physical non linearity is introduced on the formulation by the constitutive law defined as effective stress and permeability void ratio functions. Based on this numerical model, a computational system named AC-3.0 was developed, which has been verified and validated in terms of the temporal variation of the void ratio distribution throughout the soil layer, by comparing the numerical results with analytical and numerical solutions found in literature for some specific scenarios. Knowing the void ration distribution,it is possible to obtain secondary variables such as: superficial settlement, effective stress and excess of pore water pressure.The importance of the non-linear formulation is highlighted for the analysis of problems related to material presenting high compression and a very high initial void ratio.

Resumo em Inglês:

Abstract The inclusion of grade uncertainty for multivariate mineral deposits is of great importance for the correct management of subsequent decisions involved in mining planning. Mapping grade uncertainties allows maximization of profit and resource extraction. In this article, the co-simulation turning band algorithm is applied with the aim of predicting multivariate grade uncertainties. Moreover, a probabilistic analysis in long term mining sequencing is proposed in order to select the best given grade scheduling uncertainty derived from the simulations. A case study in a phosphate mine shows that the correlation of co-simulated variables honors the original data and there is an improvement in the project by an increase in Net Present Value (NPV) planning considering grade uncertainties. A comparison is performed with the results derived from the selected schedule and the results using the model based on kriged grades.

Resumo em Inglês:

Abstract A significant cost in the operating budget of most mining operations arises from purchasing and maintaining haulage trucks. Recently, in-pit crushing and conveying (IPCC) has been subject to research because of its potential to reduce haulage costs. The objective of this study is to identify early on in a project, by means of a decision-making method, whether or not the semi-mobile IPCC (SMIPCC) is an appropriate alternative to the conventional truck haulage method on the loading and hauling approaches. This method is based on cost analysis and the evaluation of environmental impacts, being successfully tested at an existing open-pit mine, where the results indicated that the IPCC was the most cost-effective option for the operation. Although the IPCC's initial CAPEX was 60% higher than the conventional approach, the IPCC's OPEX was 43% lower, resulting in a 28% reduction of the life-of-mine net present cost (NPC).

Resumo em Inglês:

Abstract To optimize a mining project, it is necessary to deal with several technical aspects and constraints, such as orebody modelling, reserve estimation, blending strategy, optimal and operational pit designs, cost control, environmental issues, among others. In this sense, locating surface infrastructures is one of the most critical mine planning concerns, as approximating these facilities to the pit in order to reduce the operational costs, might interfere with future pit expansions in new favorable scenarios. In such cases, impacts on the project's net present value (NPV) are inevitable and must be technically dealt with, evaluating alternative scenarios to propose a strategy that increases profitability. The aim of this study is to evaluate, through NPV comparisons, different constrained scenarios, under geological uncertainty, determining the possibility of moving the constraints from their current position and/or defining priorities measuring the impact that each of them represents on the project's profitability. The methodology is applied to a phosphate mine, to determine the best alternative from a long-term mine planning perspective. The use of the hybrid pit approach, applied to a simulated grade model, allowed to identify the occurrence of probability zones within a mathematical pit, providing further information to support decision making regarding infrastructure relocation.

Resumo em Inglês:

Abstract Mining activities worldwide are subject to serious geotechnical accidents involving tailings dams. Therefore, many studies have focused on tailings dewatering before their deposition. This article studies the rheological properties of flocculated and thickened nickel tailings in order to determine the effect of the initial solid concentration and type of rheology modifying agents (two anionic polymeric flocculants) on their stability for disposal in dams. The sediment was submitted to rheological tests, with the vane technique, and slump tests, to obtain information about static and dynamic yield stress and slump height, respectively. The results showed a strong influence of the initial solid concentration and the polymeric flocculant on the particle aggregation. Both particle cohesion and yield stress of the sediment increased, reaching static yield stress of around 1,400 Pa. Both flocculants were efficient in thickening by batch sedimentation, allowing water recycling in the range of 70-90% with turbidity less than 100 NTU and the production of sediment with static yield stress much higher than specified for mineral paste.

Resumo em Inglês:

Abstract The strategic mine plan is a crucial step for the success of mining companies, and for its development, it is necessary to use a number of inter-related variables that are usually estimated independently. These variables include operational data that is traditionally isolated in information islands between the different departments in the mine or they are consolidated into individual models. This reduces the holistic view of the deposit, thereby causing a negative impact on the results of the strategic planning itself. In order to improve the process and to maximize the production and/or value of a mining project, there needs to be an integration of the geology, the mine plan, the processing and the geometallurgy data. In order to accomplish this, a new methodology is proposed for the creation of a technological model. This model can be interpreted as the consolidation of the different models required for a better understanding of the geological and technical information of the deposit. This concept was developed and applied at a copper and gold mine site located in Brazil. Based on the evaluation of different blasting and mill productivity scenarios through a pit-to-plant approach, it was possible to obtain operational short-term gains such as a 10.7% increase in the plant production rate and a 2.2% increase in the crusher's feed rate with little or no capital investment.

Resumo em Inglês:

Abstract Nowadays, Nexa Resources (ex-Votorantim Metais) operates two zinc mines in Brazil, represented by the Vazante unit in Vazante - MG and the Morro Agudo unit in Paracatu - MG. The present study was carried out at the Vazante unit, where zinc concentrate is produced from a silicate ore called Willemite (Zn2SiO4) through froth flotation processes. The two main objectives of the study were the determination of the maximum zinc recovery that could be obtained in flotation bench tests with specific controlled conditions and the mineral characterization of the tailings generated, using a SEM/EDS (scanning electron microscope with energy dispersive x-ray spectroscopy) with MLA (mineral liberation analyzer). The flotation results showed a maximum recovery of 91.91 % with 1.68 % of zinc in the tailings after an eleven-minute flotation. Considering the mean results of all the tests, the maximum zinc recovery obtained was 91.07 % with 1.75 % zinc grade in the tailings. Mineral characterization analysis showed that zinc minerals besides Willemite, such as Gahnite and Franklinite are present in the zinc tailings. In addition, the analysis demonstrated that the Willemite present in the tailings is very fine (80 % < 0.015 mm) and well liberated. With no liberation problems, it was concluded that the main reason responsible for preventing zinc recovery to increase even more along the flotation tests was the presence of the extremely fine Willemite minerals. The test results showed that, to increase zinc recovery, two main processes needed to be considered. The grinding process, that will need to be improved and carefully revised to reduce Willemite fine grain size generation; and the flotation process, regarding bubble formation, reagent addition, resident time and a redesign of flotation machines, aiming to increase the recovery of extremely fine Willemite ore particles.

Resumo em Inglês:

Abstract The transport distance in a mining operation strongly influences a mine operation revenue and its operational cycle because it is a fundamental part of the total mining costs. Generally, the transport route is determined based on an engineer's practical knowledge, which does not consider any mechanism to optimize the possible routes to be taken. In an attempt to establish a methodology for calculating the path that results in minimum costs to transport the mined block to its destination, the Dijkstra methodology is applied to a tree graph analysis, where the mining blocks are analysed as nodes of the tree. The transport cost is reflected as the arc of the graphs, which can use the Euclidean distance or the transport time for the calculation of the minimum path. The result obtained from the Dijkstra algorithm provided a non-operational route; to overcome this problem, an adjustment was performed through non-parametric equations. In this manner, it was possible to determine the transport costs for each block of the model. The paths based on Euclidean distance and transport time showed a tendency to increase for deeper mining regions. Identifying areas of largest growth and correctly quantifying their values increase the efficiency of mining planning.

Resumo em Inglês:

Abstract In this article, we present the results of the mineralogical quantification of airborne dust from an urban area located in the Brazilian state of Minas Gerais in the vicinity of a gold mine. Three samples were collected at different points to assess spatial consistency. Results showed that the mineralogy, in relation to both major minerals and accessory minerals, is very similar for all samples, being predominantly composed of muscovite and quartz, which together account for around 60% to 75% by weight. The accessory minerals are clinochlore, albite, dolomite, calcite and kaolinite and the averages for each range from 4% to 13%. The only trace mineral with concentration below 1% was pyrite which has a concentration below 1%. The results provide an indication that the mining area is not the sole source of local dust, although the mine's contribution is significant.

Resumo em Inglês:

Abstract Pre-concentration consists of the preliminary discarding of a fraction of the mineral processing plant feed which contains little or none of the mineral of interest, reducing the mass to be processed in downstream operations (e.g. milling, concentration and dewatering), as well as the capital and operational costs. In this context, this study investigates the performance of density and sensor-based sorting separation methods in the removal of carbonate gangue of a zinc ore, in size fractions typical of crusher products, using sink and float tests with heavy liquids, jig stratification and laboratory scale ore sorting tests using an X-Ray Transmission (XRT) sensor. The best results were obtained through sink and float in heavy liquids, which indicated the possibility of discarding 30% of the feed mass, removing over 60% of the carbonates (CaO and MgO) and losing only 2% of the zinc. The ore sorting tests also presented positive results, with approximately 93% of metallurgical recovery in 70% of the mass for both size fractions tested. The jig stratification results were worse, since the zinc content discarded with this method was high. The results indicate significant reduction potential for Capex and Opex costs using pre-concentration strategy.

Resumo em Inglês:

Abstract This article deals with a study performed at the Experimental Mine of the Research Center of Responsible Mining of the University of São Paulo, to examine the correlations between geological environment, blasting parameters and energy consumption in the primary crushing phase. The research is designed to appreciate the relationships between the energy provided for size reduction and the resistances to size reduction. For this purpose, Key Performance Indicators (KPIs) are used to describe the possible improvements on the energy consumption due to crushing. Four blast tests were performed: for each blast, KPIs were recorded regarding the blast design, the particle size distribution, the real power energy consumption at the primary crushing unit and its rate of utilization. The results show that energy consumption at the primary crusher is a sum of two components: energy directly involved in crushing the rock, and additional energy used for winning the inertial resistances of the moving parts of the crusher. We show how explosive energy and delay times influence the production of coarse fragments that jam the crusher, therefore influencing machinery stops and inertia loads related to putting the jaws back into movement.

Resumo em Inglês:

Abstract The present article focuses on the study of different physical-mechanical parameters; it presents the results of a preliminary investigation aimed at experimental characterization. To simulate the mechanical behavior of the rock, a reference material needs to be chosen. The reference material selected is Sandstone, which is commonly used in this field of study. The behavior of sandstone from the region of Hassi Messaoud, which is well known for its petroleum operations, deals mainly with different mechanical sandstone properties and their varying strengths. The relationships between different depths and both of the mechanical sandstone properties were evaluated. As a result, useful relationships were found for different depths and the following properties: uniaxial compressive and triaxial test, Young's modulus and Poisson ratio.