Resumo em Inglês:

Abstract This article analyzes sleeve connections between circular hollow sections. This type of connection is composed of two tubes connected by bolts to an inner tube with a smaller diameter, and explores the efficiency, aesthetics and resistance of hollow sections subjected to tension and compression. In previous researches, sleeve connections with aligned and crossed bolt dispositions and under axial tension were studied. Herein, the behavior of sleeve connections with aligned bolts and under compression was analyzed. A model to represent the connection using the finite element method was developed, which allowed a numerical analysis with geometric property variations. In the numerical/parametric results, bearing failure was observed in all cases, either in the outer or inner tube. Limiting the number of bolts to 6 and considering that connections have a lower outer thickness than the inner tube, a formulation was proposed to determine the ultimate bearing capacity of sleeve connections under compression and with bearing failure.

Resumo em Inglês:

Abstract The purpose of this article is to evaluate the shear strength parameters of mixtures of sandy soil with high asphalt emulsion contents for their use in geotechnical structures, such as zoned earth dams, embankments, etc. The methodology adopted consisted of: collecting and characterizing samples of sandy soil to be laboratory tested; compacting the mixtures between soils and asphalt emulsion with contents varying between 13% and 28% in weight by using different compaction methodologies; and performing direct shear tests to evaluate the parameters governing the shear strength behavior of the manufactured mixtures. Results showed that the use of a high asphalt emulsion content contributed to greater homogeneity of the mixtures. It was also found that the presence of residual asphalt gave a bilinear behavior to the sandy soil for the failure envelopes obtained from direct shear tests. At normal stresses usually less than 100 kPa, the mixtures present a cohesive intercept due the existing residual binder, while for normal stresses higher than 200 kPa, the mixtures presented a friction angle equal to the matrix of sandy soil used.

Resumo em Inglês:

Abstract Fundamental Sampling Error (FSE) is generated whenever a sample is taken from a lot of particulate material and is caused by an intrinsic characteristic of every mineral deposit: the constitutional or intrinsic heterogeneity of the ore. FSE is the only error that can never be eliminated in sampling processes, but it can be reduced to acceptable values. The optimisation of sampling protocols is based on the minimisation of FSE and is essential to reduce the deviations of grade estimates for mine planning, process control and mine-to-mill reconciliation. In order to calculate minimum sample masses and to optimise sampling protocols, heterogeneity studies have been developed. The original heterogeneity test (HT), proposed by Gy (1967) and Pitard (1993; 2009), is an experimental method of obtaining the intrinsic heterogeneity (IHL). Most of the heterogeneity studies available in Brazilian literature have been performed on gold deposits, which have higher intrinsic heterogeneity due to the nugget and cluster effects and low grades, unlike base metal deposits. Nickel ores have never been the focus of heterogeneity studies in Brazil or worldwide. Therefore, the factors that compose IHL have never been validated for nickel ores, which was the objective of this article. Based on the results of the heterogeneity test performed on a nickel ore from Niquelandia, Brazil, the standard deviations of FSE were calculated at each stage of the sampling protocol. An optimised protocol is proposed herein, in which the total deviation of FSE is below the maximum value recommended by Pierre Gy’s Theory of Sampling (TOS).

Resumo em Inglês:

Abstract This study aims to evaluate the influence of the 11.6Li2O-16.8ZrO2-68.2SiO2-3.4Al2O3 (mol%) glass-ceramic addition (LZSA, 7 to 21 vol%) on the erosive wear of alumina in comparison to values of pure alumina obtained from the literature. Thus, composites were prepared from three commercial alumina of different initial particle sizes. Specimens were obtained by uniaxial pressing. Sintering temperatures and holding times were found to be different for each composite. The erosive wear test was carried out in an apparatus based on the standard ASTM G 76-4. The volumetric erosive wear (T vol) was correlated to the initial mean particle size of alumina, LZSA glass-ceramic content, average grain size of sintered alumina (AGS), porosity (P), elastic modulus, fracture toughness, natural defect size, and fracture energy based on a correlation matrix of statistical analyses. The experimental data of Tvol fit very well with P and AGS, individually, in a 3rd degree equation, except for composite AF21. Composite AF21, i.e. 21 vol% LZSA added to 0.5 µm mean particle size alumina (AF, fine alumina) and sintered at 1470 oC for 3 h, showed interesting results of T vol(2.05 × 10-8 m3·kg-1) related to the other investigated compositions, which varied from 1.90-4.37 × 10-8 m3·kg-1, and those existing in literature (0.55 × 10-8 to 10.78 × 10-8 m³·kg-1), mostly when considering the lower sintering temperature (1470 against 1600 oC). Thus, although the AC7 composite had shown the lowest Tvol value (1.90 × 10-8 at 1600 oC/7 h), the composite AF21 can be considered as the best result because of its lower sintering temperature and holding time (2.05 × 10-8 at 1470 oC/4 h). The formation of a viscous liquid phase, which crystallizes during the controlled cooling in the microstructure of the LZSA/alumina-based composites, improves the erosive wear of the alumina.

Resumo em Inglês:

Abstract The objective of the present study was to evaluate the effect of high additions of petroleum coke on the rheological properties of coking coal and the quality of cokes produced on pilot scale at the Usiminas R&D Center. For this purpose, blends using petroleum coke additions of 5%, 10%, 20%, 30% and 40% were produced. The results showed that the blends were able to satisfactorily absorb up to 30% of petroleum coke, keeping the quality (DI, CRI and CSR) similar to the industrial mixture. The observed main textural components were: mosaic, fragmentary, fusite and anisotropic inert. In general, before CRI, cokes showed good cohesion, with the petroleum coke having been absorbed by the coke matrix. After the reaction with CO2, there was verified a preferential consumption of the textures fusite, fragmentary and anisotropic inert due to the Boudouard reaction, besides the deterioration of the interfaces between the petroleum coke and coke matrix. In addition, the results showed that the increase of mosaics contributes to the increase of cokes DI15-150 and CSR. Finally, for the coal blend employed, it is suggested the utilization of a maximum of 30% additions of petroleum coke.

Resumo em Inglês:

Abstract The discrimination between pores and cracks is an important step in the microstructural analysis of iron ore pellets. While the porosity is fundamental during the reduction process in blast furnaces, cracks are strongly detrimental to the mechanical strength. The usual image processing tools cannot automatically discriminate between these two types of features, especially in 3D images obtained, for instance, with x-ray microtomography (microCT). As pores and cracks have essentially the same x-ray absorbance, they cannot be discriminated by a simple intensity threshold. Given the complex shapes in 3D and the presence of many connections between pores and cracks, shape discrimination is not successful either. Thus, this article proposes the use of Deep Convolutional Neural Networks (DCNN) to discriminate between these 2 classes of discontinuities. The well-known U-NET architecture was employed. The network was trained by manually outlining representative objects of the 2 classes in a few layers of the 3D image. After optimization of the training parameters, the network was applied to the full image, successfully discriminating between pores and cracks. The trained network was then applied to the images of different pellets with good results. However, some residual errors are present. These characteristics are analyzed and possible solutions are proposed.

Resumo em Inglês:

Abstract The stability of colloidal suspensions of engineered nanoparticles in the environment is of great interest for the risk assessment and treatment of hazardous materials. The relevance of this study is due to the evidence that engineered nanoparticles have been produced and used in commercial products in large scale, especially ZnO and TiO2, which are transported through the environmental components interacting with soil and water, representing the high potential impact on the ecosystems. In this research, we newly investigated the influence of nanoparticles of zinc oxide (NPZnO) on the behavior of nanoparticles of titania (NPTiO2). The impact of parameters such as pH, zeta potential, ionic strength, electric conductivity, suspended nanoparticles size of the colloidal suspensions containing hazardous nanoparticles on its stability, were studied using experimental and theoretical approaches. Leaching experiments were carried out within a sandy soil column model. It was found that the NPTiO2 in suspensions enhance the stability of the nanoparticles colloidal suspensions, keeping higher nanoparticles concentrations, while NPZnO promotes rapid aggregation, improving the soil particle collector efficiency with a lower concentration in equilibrium in the colloidal suspension, which can be used for promoting environmental impact attenuation and mitigation.

Resumo em Inglês:

Abstract Silicate rock Verdete, collected in the central region of Minas Gerais state (Brazil) and composed mostly of micas (glauconite and muscovite) and tectosilicates (K-feldspar and quartz), was hydrothermally treated with several reactants in order to release and recover potassium. The hydrothermal products were characterized by flame photometry, XRD, XRF, SEM and EDS. Treatment with sulfuric acid was effective to break the crystal lattice of micas before 1 h of reaction and recovered 24% of potassium in the form of sulfates. The K-feldspar appears to have remained intact during the process. Treatment with a Ca(OH)2 (86 wt.%) - CaCO3 (14 wt.%) mixture did not consume the micas, but K-feldspar was gradually consumed over the 24 h reaction period. The K recovery was probably due to a concurrent hydrolytic framework dissolution of K-feldspar mediated by OH− ions and by the exchange of K+ with Ca2+. The K-bearing species are carbonaceous materials with variable K+/Ca2+ ratios, such as K2Ca(CO3)2.

Resumo em Inglês:

Abstract If not managed properly, mining waste can be detrimental to the environment. In addition, sewage treatment plants produce sludge, a biowaste rich in organic matter which is often sent to landfills. The present study evaluated the use of sewage sludge as an amendment for mine waste from a basalt quarry as an alternative to the use of soil from borrow areas during environmental restoration. An ex situ experiment was developed at the Federal University of Rio Grande do Sul - UFRGS. The experimental delineation compared the addition of two sources of organic matter (sewage sludge - SS and cover soil from that same region - CS) to basalt waste rock (BWR) against the sole use of cover soil, which a current restoration technique. The graminoid Avena strigosa (black oats) and soil fertility tests were used as indicators of soil conditions. Amending BWR with SS led to the best physical and chemical conditions and the highest production of dry matter in comparison to the use of CS as amendment or its single use as cover soil. These results show that mixing SS to BWR can be used as a substitute for cover soil during the environmental restoration of basalt quarries, further contributing to the final disposal of these materials.

Resumo em Inglês:

Abstract Developing mine sequencing involves a number of factors and a large amount of information, and consequently the profitability of the project will strongly depend on the production schedule. A mining project may be conditioned to non-optimal sequencing, which may affect the economic results of the project and also lead to an inadequate utilization of the mineral resources. The conventional method of mining sequencing is divided into three main steps: first, the delineation of the final pit; second, subdivision of the final pit in operational pushbacks (mining advances) and third, sequencing the blocks in each of these pushbacks, taking into consideration mine, processing plant and market capacities. However, there are some aspects that are not usually incorporated in production scheduling, including ore mining below groundwater level. The objective of this study is to demonstrate the relevance and impact on the results of the Net Present Value (NPV) from groundwater level as a constraint related to the need for its drawdown, also considering grades and Stripping Ratio (SR) variability during mining sequence for a phosphate mine. The results show a difference of U$ 140 million for the evaluation considering and not considering groundwater level, without considering other restrictions.

Resumo em Inglês:

Abstract One of the most characteristic aspects of artisanal mining is the lack of geological exploration. Going into production without previous exploration is here defined as a gambling scenario. The present study intended to quantify the risk associated to such gambling by analyzing the operations of an area of artisanal underground gold mining in central Chile. To quantify the risks and the probable outcomes, a risk analysis technique called Event Tree Analysis has been applied. This technique is based on the analysis of possible multiple outcomes of single events or decisions and the probability of occurrence of each. Results show that chances of negative vs. positive revenue are 83% vs. 17%, with an order of magnitude of difference between worst-case and best-case scenarios.

Resumo em Inglês:

Abstract Bauxite mining has been carried out around Poços de Caldas, Minas Gerais, since the 1940s. Companies operating in the region pioneered land rehabilitation in Brazil, conducted since the early 1980s. Different procedures of recontouring, runoff drainage, soil preparation and vegetation planting were employed. This research aims to evaluate current environmental rehabilitation practices employed in the region, in order to identify possible deficiencies, investigate probable causes of these deficiencies and prevent recurrence of failures, thus avoiding rework and additional costs to deliver outcomes satisfactory to land owners. Areas with different ages of rehabilitation were studied. The practices adopted in recently rehabilitated mines and in the final phase of operation were evaluated through a problem identification procedure, based on field observations, document analysis and interviews. Some unsatisfactory results were found related to ground terracing, drainage systems, block sliding, soil sampling, soil preparation, planting of vegetation and monitoring of the recovered area. Improvements are proposed, on the basis of good practices, that even if more complex and laborious, can result in future savings, as they enable, in addition to avoiding rework, the fulfillment of contractual obligations to landowners and regulatory bodies.

Resumo em Inglês:

Abstract The flotation process currently considered for apatite concentration from the Santa Quitéria phosphate deposit (Brazil), involves bulk flotation of apatite and calcite with anionic collector at pH=10 followed by calcite flotation at pH=5.5, adjusted with H3PO4. Although this concept is efficient from the point of view of separation between apatite and calcite, the intensive use of inorganic acids causes ion accumulation in the process water, especially Ca2+ and PO4 2-, which leads to problems in the flotation stage as well as in the environment. CETEM has been studying a process for the separation of carbonate minerals and apatite that involves the use of carbonic gas injected into the bubble generation system of flotation machines instead of inorganic acids. The aim of this study was to evaluate the effect of Ca2+ ion concentration on the water during the calcite flotation stage of the Santa Quiteria phosphate ore, between 6 mg/L (standard test) and 670 mg/L (maximun concentration) on the flotation performance in terms of P2O5 grade and its loss and the CaO/P2O5 ratio (RCP). The results indicated a reduction in the selectivity on the flotation of calcite from apatite for Ca2+ concentrations from 6 mg/L to around 285 mg/L. Despite this, the results obtained in this study indicated that the process based on the application of CO2 for the separation of calcite and apatite may be a technical alternative that causes less impact in flotation performance for the phosphate concentration ores with carbonated gangue.

Resumo em Inglês:

Abstract Long-term mining planning is a complex process which involves a large number of variables and uncertainties. Traditional discount cash flow (DCF) is usually used in the evaluation of mining projects. DCF includes net present value (NPV), internal rate of return (IRR), and profitability index (PI). A sensitivity analysis is usually carried out to evaluate the impact of the main variables on the project. Another way to measure uncertainties is through the Monte Carlo simulation (MCS). The objective of this study is to evaluate and compare the DCF methods and measure uncertainties through sensitivity analysis and MCS in the evaluation of mine sequencing. A case study of a phosphate mine project was used to chart the comparative study. In the results, NPV and uncertainty analysis through MCS were more consistent.

Resumo em Inglês:

Abstract For the Brazilian iron ore mines, the presence of caves presents a challenge, since most of them are located within the ore deposit. The National Environment Commission (CONAMA 347 Resolution/2004) establishes that the speleological heritage, as well as its area of influence, cannot sustain irreversible environmental impacts. The physical integrity of caves adjacent to mining operations is an issue of pivotal importance to be scrutinised in studies towards the delimitation of the cave’s protection radius. This article presents the study of various models of correlation between the RMR and Q systems used for the stability assessment of natural iron ore caves. In order to study a correlation between the RMR and Q systems, the most popular rock mass classifications, and their application as a validation tool, a selection of measurements of Q and RMR, organized in a database from seven natural caves of ferruginous lithology, are submitted to a study and statistical analysis. An empirical equation was obtained from the data, using a simple linear regression. The result of the regression was compared with selected correlation equations and the best fit for the data was chosen. The best fit was the Rutledge & Pearson correlation equation, which presented the best combination of R² and S, after the equation created on basis of the real values for RMR, though the other equations have results similar to it. As the results were quite similar, the recommendation still is that correlations should be used with caution, and associated to other methods and field analysis.