Resumo em Inglês:

Abstract In nature, metal ores such as iron, lead, aluminum and others are found in an impure state, sometimes oxidized and mixed with silicates of other metals. During casting, when the ore is exposed to high temperatures, these impurities are separated from the molten metal and can be removed. The mass formed by these compounds is slag. Slag is the co-product of the smelting of ore to purify metals. It may be considered a mixture of metal oxides, but may also contain metal sulphites and metal atoms in their elemental form. After it is reprocessed to separate the metals contained, the co-products of this process can be used in cement, rail ballast, road paving and various other purposes. The objective of this research work is the presentation of the chemical and mineralogical characterization tests of the silicon-manganese iron slag with the purpose of reusing the co-product as rail ballast. X-ray diffraction tests, quantitative chemical analyzes, scanning electron microscopy and free lime content were prepared for these characterizations. The results of these tests showed the technical feasibility of using slag as rail ballast.

Resumo em Inglês:

Abstract The circular hollow sections (CHS) are being widely employed in steel structures around the world, increasing the development of new researches. This article proposes an innovative connection model for circular hollow sections that facilitates and reduces the assembly cost of hollow section structures. The proposed connection is a tube sleeve, used to splice two tubes, composed of an inner tube with a diameter smaller than the connecting tubes, which is connected to the outer tubes by bolts passing through both tubes. This connection can be a cheaper and easier alternative to flange connections, which are widely used in large span tubular trusses. The connection was tested in laboratory under tension loading. The tests made it possible to identify the influence of stress distribution on tubes and the need for the use of a shear lag coefficient. The results of the ultimate load capacity demonstrated the viability of the tube sleeve connection use.

Resumo em Inglês:

Abstract Here-in, a numerical analysis based on the Finite Element Method (FEM) is proposed in order to investigate cold-formed steel back-to-back double angle structural behavior under compression. Considering non-linear analysis, an investigation was performed to analyze the influence of some aspects, such as the loading condition (concentric and eccentric axial compression), the boundary conditions, the global slenderness, the global and local geometric imperfections, the angle thickness and the number of packing plates. The numerical results signalize that the compression strength obtained in accordance with the standards ABNT NBR 14762:2010 and ANSI/AISI S100 (2012) may be quite conservative, mainly in the lower global slenderness cases. Additionally, the connection spacing (bolted connection with stitch plates in-between the angles) and the presence of a connection at mid-length change the buckling mode, as well as cause a significantly increase in the axial compression strength of the member. The numerical analysis also indicates that the design proposed by ABNT NBR 8800:2008 for the case involving angles under compression connected by one flap can also be applied to cold formed steel angles.

Resumo em Inglês:

Abstract Punching shear is a possible type of failure that occurs in reinforced concrete flat slabs, which can develop with an ultimate load below flexural capacity. Several researchers have studied the punching resistance of flat slabs over recent years. Although they have made great advances, there are codes that show different approaches to a singular design. Some codes show that there exist contradictions, even in the simplest situations, such as concentric loads. Most codes prescribe empirical expressions based in a theoretical model to analyze punching strength, but for flat slabs with holes around the column and shear reinforcement there are divergences between codes, justifying research in this area. This paper presents an experimental analysis of nine square reinforced concrete flat slabs under concentric loading (width: 1800 mm; thickness: 130 mm). The main variables used in the tests were: a) two square openings (150 mm) adjacent to the smallest side of the column and b) the use of shear reinforcement containing 3 layers, with 6 or 8 elements in each layer and radially distributed around the column. The research concludes that openings adjacent to the column affect punching shear strength, while the correct use of the shear reinforcement can minimize and even compensate this loss.

Resumo em Inglês:

Abstract A preliminary study on a petrochemical harbor as a potential source of polycyclic aromatic hydrocarbons (PAH) to surface sediments of Guajará bay, located in Belém City, Pará State, Brazil, over the last 10 years is presented here. The 16 priority USEPA PAH were identified and quantified. Surface sediment samples, collected at 5 sites in the bay, near Miramar Petrochemical Harbor (TEMIR), were extracted and analyzed by high performance liquid chromatography with a diode array detector. Total PAH concentration ranged from 533.0 to 3123.3 ng g-1 dry weight with a mean concentration of 1091.9 ng g-1. The most contaminated places were those where muddy sediments were found with highest concentrations of organic matter. The priority PAH with low molecular weight represented 54.4% of the total abundance and indicate that the main source of contamination of the sediments was petrogenic, indicative of the relevant contribution of the petrochemical harbor activity to the input of PAH to Guajará bay. However, pyrolytic PAH coming from fuel combustion, household waste combustion and untreated sewage discharge are also potential contamination sources to this environment.

Resumo em Inglês:

Abstract This work aims to reduce the energy consumption and thus increase the availability of blast furnace compressors of a steelmaking company, located in Alto Paraopeba region in Minas Gerais state, Brazil, through the elimination of waste points in the compressed air distribution. In order to develop this work, an ultrasound test in the compressed air line was performed to identify and quantify leaks in the flow. Once the leaks were identified, they were eliminated through corrective maintenance and improvements, and then the energy consumption scenarios before and after the improvements were compared. As a result, the average monthly electricity consumption in the reporting period decreased by 57.2%. In addition, one compressor was set aside in stand-by condition, as in the original plant. Thus, one can prove the efficiency in eliminating of waste points in compressed air distribution, since the reduction of energy consumption is important for the company to remain competitive, as the cost of electric energy affects the final price of the final products.

Resumo em Inglês:

Abstract The coolant delivery technique known as Minimal Quantity Lubrication (MQL) has been employed in machining since the end of the 20th Century and has gained considerable evidence in the last years as a viable alternative to the use of the conventional coolant technique (flood). Due to the low oil flow rate delivered by the MQL technique in grinding operations, that generally varies from 20 to 240 ml / h in relation to near 600,000 ml / h flow rate of the conventional coolant technique, the MQL technique provides a reduced risk for human health and environmental damage associated with the use, maintenance and disposal of cutting fluids. In this context, this study was carried out to evaluate the application viability of the minimum quantity lubrication coolant technique under different flow rates in the plunge cylindrical grinding of ABNT 4340 steel with an aluminum oxide wheel. Three flow rates were tested: 30, 60 and 120 ml/h. Grinding trials with the conventional coolant delivery method were also tested for comparative purposes. The output variables used to assess the efficiency of the MQL technique in this work are: roughness, roundness and hardness of the workpiece. Grinding wheel wear and power consumption were also monitored. The results showed that, despite the higher values of roughness and roundness of the workpiece, as well as the grinding wheel wear, the values of these same parameters obtained after machining with the MQL technique were close to those obtained after machining with the conventional technique. No thermal damages and cracks on the machined surface, or even below the machined surface, were observed after grinding ABNT 4340 steel irrespective of the coolant-lubrication condition investigated. The results showed that the MQL with 120 ml/h can be an alternative coolant technique due to cleaner environment and lower consumption of fluid in grinding under the conditions investigated in this work.

Resumo em Inglês:

Abstract This work was developed in order to validate a simplified computer simulation method for application in the drawing processes. The results of tensile tests on AISI 1004, AISI 1020 steel and copper were compared to those of computer simulations performed using the Deform-3D TM software. Each specimen was assumed to be an elasto-plastic material and was meshed with 50,000 finite elements. Young's modulus and Poisson's ratio were the only material properties considered in the elastic region; the parameters of Hollomon's equation were used in the plastic region up to constriction. A strain rate of 1x10-3 s-1 was applied during the simulations. In the plastic region, up to the point of constriction, the curves obtained from the simulations showed reasonable correspondence to those determined from physical testing. However, the former diverged from the latter in the elastic and elastic-plastic transition regions. This divergence indicates that microstructural factors may have a greater influence in the transition region than in the plastic region. Moreover, the correlation obtained in the plastic region indicates that the proposed method has the potential to be applied in drawing processes.

Resumo em Inglês:

Abstract The presence of copper-bearing minerals is known to bring on many challenges during the cyanidation of gold ore, like high consumption of cyanide and low extraction of metal, which are undesirable impacts on the auriferous recovery in the subsequent process step. The high copper solubility in cyanide prevents the direct use of classical hydrometallurgical processes for the extraction of gold by cyanidation. Additionally, the application of a conventional flotation process to extract copper is further complicated when it is oxidized. As a result, an acid pre-leaching process was applied in order to clean the ore of these copper minerals that are cyanide consumers. The objective was to evaluate the amount of soluble copper in cyanide before and after acidic cleaning. From a gold ore containing copper, the study selected four samples containing 0.22%, 0.55%, 1.00% and 1.36% of copper. For direct cyanidation of the ore without pre-treatment, copper extraction by cyanide complexing ranged from 8 to 83%. In contrast, the pre-treatment carried out with sulfuric acid extracted 24% to 99% of initial copper and subsequent cyanidation extracted 0.13 to 1.54% of initial copper. The study also showed that the copper contained in the secondary minerals is more easily extracted by cyanide (83%), being followed by the copper oxy-hydroxide minerals (60%), while the copper contained in the manganese oxide is less complexed by cyanide (8% a 12%). It was possible to observe that minerals with low acid solubility also have low solubility in cyanide. Cyanide consumption decreased by about 2.5 times and gold recovery increased to above 94% after acidic pre-cleaning.

Resumo em Inglês:

Abstract Herein is presented the results of a study on the hydrometallurgic extraction and recovery of aluminum and silicon by leaching of kaolinitic clays with HF. The studied extraction parameters were: temperature, reaction time, solid/liquid ratio, concentration, and precipitating agent mass. In the leaching process, mineral dissolutions near 100% were obtained when working at 348 K, solid/liquid ratio 2% w/v, HF 12% v/v, for 120 minutes. The HF leach liquor generated from the dissolution of kaolinitic clays contains H2SiF6and H3AlF6. Studies were conducted to recover the two valuable fluorides as K2SiF6and Na3AlF6by precipitation with alkaline salts from the leach liquor. Phases of precipitated fluorides were identified by XRD and surface morphology by SEM. The purity of the K2SiF6precipitate was 98.8%, whereas for Na3AlF6, it was 89.3%. Also, both synthesized solids are of high commercial value due to their industrial applications.

Resumo em Inglês:

Abstract The use of alumina as a reinforcement in metallic and ceramic matrix is well-known. The purpose of this study was to investigate the effect of alumina addition according to its amount on the microstructural and mechanical behavior of tricalcium phosphate ceramic (TCP), more specifically the β-TCP. Although β-TCP has excellent bioactive and biocompatible properties, it presents low fracture resistance and load bearing capacity, which limits its use in the monolithic form. The route used for the β-TCP/alumina composite production was powder metallurgy. The powders were milled in a high energy ball mill with the following parameters: 5, 10, 15 and 20 hours, mass/sphere relation of 1:20 and speed of 150 rpm. After the milling process, the powders of both compositions were uniaxially pressed and sintered. Two of the compositions were processed containing 90% and 50% of β-TCP, respectively. The results indicated that composition 1 with a smaller percentage of alumina in its microstructure presented 62.4 % smaller particle size after the high energy ball milling process, which provided higher densification after pressing and sintering. These results implied in increased mechanical resistance, with 4.6 GPa of elastic modulus and 140 MPa of compressive strength, against 3.6 GPa of elastic modulus and 117 MPa of compressive strength obtained in composition 2.

Resumo em Inglês:

Abstract Process analyses foster opportunities for identifying losses during the production process and consequently, provide courses of action to enhance the process with operational parameters that are compatible with the targeted results. In this study, a thermochemical model was developed in order to monitor the performance of coke-based blast furnaces, focusing on tools for calculating and graphically displaying parameters that facilitate interpretation of the internal phenomena. To apply the model, a database was prepared based on operational simulations of blast furnaces. The input parameters for the model consisted of the properties and consumption of raw materials and the mass and thermal balances of the process. The thermochemical model is based on the calculation of the degree of reduction of the metallic burden in the preparation zone, defined as the omega factor. It was found that the omega factor varies significantly with the CO/CO2ratio and %H2of the top gas. The results obtained by applying this model were coherent, thus validating it as a predictive tool for assessing the sensitivity of the omega factor, which has a major effect on carbon consumption.

Resumo em Inglês:

Abstract Initially studied was the effect of the casting mode on the electrical conductivity of AA4006 aluminum alloy sheets produced by both Twin Roll Casting (TRC) and by the semi-continuous Direct Chill (DC) industrial processes, when compared to sheets with commercial purity (AA1050) and high purity aluminum (AA1199). Then, the effects of heat treatments on the electrical conductivity of the AA4006 alloy sheets produced by TRC were also studied. Isochronous and isothermal heat treatments allowed to obtain the precipitation and solution kinetics of the intermetallic compounds. The precipitation kinetics was analyzed with the help of the Johnson-Mehl-Avrami-Kolmogorov equation.

Resumo em Inglês:

Abstract The current work presents a bibliometric discussion on articles published worldwide concerning kaolinite flotation in international journals from 1992 to 2015. In total, 39 articles were selected from Elsevier's database, SciVerse ScienceDirect. This work allowed to recognize and identify which are the thematic and methodological trends that are being used, in addition to the main collectors used in kaolinite flotation. The results show that a significant amount of articles is produced by Chinese authors, especially from 2013, as China is the second highest aluminum producer in the world, and kaolinite is the reject in the reverse flotation process of diaspore. The results showed the difficulty of working with kaolinite flotation individually and confirmed that there is scientific collaboration among authors. Bibliometric analysis showed that the reagents used in kaolinite flotation tests are mostly derived from cationic nitrogenated compounds. Additionally, best recovery results from kaolinite flotation occurred in acidic media.

Resumo em Inglês:

Abstract Tailings storage facilities are disposal systems for storing the waste products of the mining industry consisting of a slurry mixture made of soil, rock and water that remain after the mineral values have been removed from the patent ore. Tailings dams are supposed to last forever, so after their deposition, tailings can experience aging processes with physical and chemical changes depending on the interactions between local conditions and source mineralogy. The consequences of these aging processes are increased interlocking of particles and oxidation processes, sometimes making previously safely held contaminants available and mobile. Among the long-term aging processes, the natural ionizing radiation (from radioactive isotopes of the soils, cosmic rays, and also ultraviolet rays from the sun) can be considered, as proposed in the current research. Furthermore, in many countries, tailings are beginning to be re-used as backfill, landscaping material or feedstock for cement and concrete. So if any, the long-term physical and chemical modifications could affect the hydraulic and mechanical behaviour of tailings with relevant economic consequences. For these reasons, wet and dry silty samples of tailings spilled out after the failure of the Stava tailings dam (Trentino Alto Adige, Italy) were exposed to gamma rays, as an accelerated aging technique to simulate the natural ionizing radiation, and then characterized. The modifications on physical and chemical properties were observed and, despite certain chemical stability, some physical changes were observed, particularly in terms of size particle distribution, inner porosity of the particles and specific surface.

Resumo em Inglês:

Abstract The agitation intensity has a directly influence on flotation performance, lifting the particles and promoting the contact of bubbles and particles. In this paper, the energy input by the agitation on apatite flotation was investigated. The influence of pulp agitation in the flotation rate of particles with different sizes and two dosage levels was evaluated by batch testing. The flotation tests were conducted in an oscillating grid flotation cell (OGC), developed to promote a near isotropic turbulence environment. The cell is able to control the intensity of agitation and measure the energy transferred to the pulp phase. A sample of pure apatite was crushed (P80=310µm), characterized and floated with sodium oleate as collector. Four levels of energy dissipation, from 0.1 to 2 kWm-3, and two levels of collector dosage are used during the tests. The flotation kinetics by particle size were determined in function of the energy transferred. The results show a strong influence of the agitation intensity on the apatite flotation rate with both low and high dosage. For fine particles, when increasing the energy input, the flotation rate increase too, and this fact can be attributed to elevation of bubble-particle collisions. The kinetic result for the coarse particles demonstrated a reduction of the flotation rate whenever the energy input for this particle size was increased, whereby the turbulence caused by the agitation promotes the detachment of bubble-particle.