Resumo em Inglês:

Abstract Brazil has an extremely limited railroad network compared to other developed and developing countries. There are projects to expand this mesh. Knowing that the cost of implementing a railroad is high, research for solutions that allow cost reduction is of great importance. But the parameters of the materials used in the subgrade and sub-ballast layers are from other countries, which can cause the cost to increase to meet these parameters. Through strength parameters and mineralogical analysis, it is possible to use or not fine tropical soils as a layer of railway pavement. A critical analysis of the standards that are used to scale and/or verify whether a particular soil can be used in these layers was undertaken. For this, the following tests were performed: Granulometry, Atterberg Limits, Compaction, California Support Index (CBR or ISC), Expansion, MCT Classification Test (Miniature, Compacted, Tropical), Dynamic Triaxial and X-Ray Diffraction. From the results, it could be seen that although one of the soils is thin, it presented satisfactory results in relation to the use in layers of the railway pavement. It was verified that it is necessary to use more modern tests, focusing on mechanistic dimensioning for dimensioning pavement layers.

Resumo em Inglês:

Abstract Soils are particulate materials, which often stand out for their low shear strength. In most cases, this aspect justifies adapting the geotechnical project for this characteristic, which can be even more problematic in the case of soft sands, since it often occurs in superficial layers in various parts of the metropolitan region of Fortaleza. Therefore, the soil improvement procedure with the addition of small cement fractions can be crucial. The content to be adopted should be such as to bring a more economically viable alternative to the geotechnical design of a shallow foundation, for example. The present research aims to propose a modified Mohr-Coulomb envelope for artificially cemented soils. The proposal is based on the development of two functions that relate shear strength parameters (cohesion and friction angle) with the cement content. In order to assess the proposed functions, triaxial shear tests were performed on the sand with different cement contents. The adjustments presented consistent results. In addition, the proposed envelope was validated using published results encountered in literature.

Resumo em Inglês:

Abstract Clinker is the raw material used in the manufacture of cement. However, this material is very harmful to the environment, since it is estimated that for every ton of clinker produced, about 1.0 ton of CO2 is released into the atmosphere. For this reason, alternatives were sought for the use of other materials that are less harmful to the environment. This has led to the use of industrial by-products with the aim of increasing their use and thus reducing the amount of carbon released into the atmosphere. Blast furnace slag is a by-product used in the manufacture of some cementitious products. The aim of this research is to conduct a study on the use of slag as an additive for cement or concrete. The mortar samples were tested according to Brazilian, American and European technical standards. Physical, chemical and compressive strength tests were carried out which confirmed the possibility of using the slag without chemical or thermal activation.

Resumo em Inglês:

Abstract This article presents a range of mix design formulations to obtain metakaolin-based geopolymer synthesis. Geopolymer samples were synthesized from metakaolin, a 10 M sodium hydroxide solution, and alkaline sodium silicate. These three components were mixed in different proportions to form a paste which was molded in a cylindrical shape, set at room temperature for 24 hours, and demolded. The workability of the paste, the integrity of the samples, development of efflorescence, and the presence of undissolved metakaolin particles in the microstructure of the geopolymer matrix were observed. Since sodium and water play a vital role in the geopolymerization and were added at fixed proportions, a mix design was employed based on the molar proportions of aluminum, silicon, and sodium plus water. The simplex design plot was able to separate the regions of a mix of the components that showed different behaviors according to the observed responses. The dissolution of metakaolin, condensation of ortho-sialate and silicate species, which are expected to interact with each other according to the model of geopolymerization of Davidovits, can explain the observed results. “Good results” (no release of white powder, no efflorescence, no shrinkage, and no cracks) after 28 days of curing at room conditions were observed for the molar proportions 0.097 < Al < 0.112, 0.120 < Si < 0.178, and 0.711 < Na+H2O < 0.775 (Na/H2O = 0.185).

Resumo em Inglês:

Abstract The purpose of circular economy is to maximize resources efficiency. With the increase in consumption of raw materials, energy and waste generation, recycling is necessary for environmental and industrial reasons. Thus, the powder metallurgy, together with mechanical milling, stands as a new method for scraps recycling. This study aimed to produce UNS S31803 duplex stainless steel powders, with vanadium carbide (VC) addition as reinforcement, through mechanical milling. Different uniaxial compaction pressures (700, 800 and 900 MPa) were used, as well as sintering temperatures (1200, 1240 and 1280 °C) and times (1, 1.5 and 2 hours), in order to determine the best conditions. Particle size analysis, scanning electron microscopy and x-ray diffraction were used to characterize the powders. It was observed that the use of VC increased the comminution during the milling process, being obtained an average particle size of 42 μm. The highest density obtained was of 82% and hardness of 72%, in comparison with the steel from the manufacturing process. According to the analysis, it was verified that this method is viable, becoming an alternative route to reuse UNS S31803 duplex stainless steel scraps.

Resumo em Inglês:

Abstract Laterite ores, which represent around two-thirds of nickel reserves, became an important source of nickel and cobalt metals. The objective of the present study was to investigate the efficiency of a hybrid route to extract nickel and cobalt present in a laterite ore sample which was not commercially attractive to be processed through the current routes. The process efficiency was investigated through the application of different test conditions, such as roast temperature, ore sample comminution, and moisture. Chemical analysis by atomic absorption was used to quantify the metals. The solid phase’s identification and characterization were accomplished by X-ray diffraction and Scanning Electron Microscopy. The Rietveld Method was used for the mineral’s phase quantification. In terms of nickel and cobalt extractions, the most favorable condition was: particle size smaller than 38 µm, 50% sulfuric acid (wt.%), and 10% moisture (wt.%), which permitted nickel, cobalt, magnesium, and iron recoveries of 84.5%, 92.0%, and 93.0%, 27.0% respectively. These results indicate the successful application of the route. In addition, it was found that chlorite, chromite, hematite, and goethite were identified as the main nickel and cobalt carriers present in the process residue.

Resumo em Inglês:

Abstract The recovery of degraded areas is imperative for the sustainability of mining activities. The main action implemented to improve the chemical, physical and biological conditions of soils, tailings and sterile deposits is the incorporation of organic material. Biosolids (hygienized sewage sludge) are among the organic materials that can be applied. However, considering the health risk they represent, not all areas are suitable for receiving this waste. The present research sought to map the environmental suitability of the Quadrilátero Ferrífero (QF) region to assess the applicability of biosolids. For this purpose, maps were elaborated using restrictive criteria established for the safe application of this residue to the soil by means of the Geographic Information System (GIS), using the ArcGIS software, version 10.2. The established criteria were pedology, topography, hydromorphism, presence of protected areas, soil texture, susceptibility to erosion, proximity to urban areas and their overlaps to obtain the final suitability areas. For the exclusion of areas that presented legal restrictions, the criteria of protected area, areas close to water bodies, urban areas, shallow soils and a slope greater than 45% were used, as established in literature, in CONAMA 498/2020 and in the Forest Law - Federal Law 12,652 of 2012. Of the areas analyzed, 58.5% were suitable for biosolid application, equivalent to 10,858.3 ha of the 18,587 ha studied, indicating the feasibility of biosolids application in part of the QF area to be recovered.

Resumo em Inglês:

Abstract The greatest and noblest challenge of mining engineering for the present and the future of iron ore treatment could be considered as the pursuit of optimizing the use of mineral resources. The use of mining tailings, in the mineral sector itself, or in another industrial branch, meets the needs of circular economy as it increases the useful service life of this material. In order to investigate this scenario, a technological characterization of a sample from a tailings dam was carried out along with magnetic concentration tests in a Wet High-Intensity Magnetic Separator (WHIMS) to propose a possible concentration route. In relation to the characterization itself, the results demonstrated a relative density of 3.04 x 103 Kg/m3and an average superficial specific area of 3.75 cm3/g. The granulometric analysis classified the material as fine, with d90 of 0.110 mm and d50 ≅ 0.049 mm. Quartz, hematite, goethite, kaolinite and manganese oxide were identified in the sample. The test which presented the best results (66.83% Fe and 1.74% SiO2) consisted of the Rougher, Cleaner and Recleaner phases, using a 1.5 mm grooved GAP matrix, a 7,000 Gauss magnetic field, 30% solids, and water pressure at 0.5 kgf/cm2 (49.0 x 103 Pa). Finally, the conclusive results indicate that the studied material can be concentrated through magnetic concentration, keeping in mind the specifications concerning the pellet feed fines commercial product. Besides the financial gain, the activity prolongs the durability of the tailings dam and reduces the environmental impacts associated with these structures.

Resumo em Inglês:

Abstract The Magnetic separation of ultra-fine ore particles has always posed a challenge to the JONES/WHIMS process. Despite many advances in this technology, no effective improvement has been made to its core component: The Magnetic Matrix. The current approach to separate ultra-fine particles teaches that the gap of the matrix and its teeth size must be smaller than usual in order to accommodate the small size of the particles. However, practice proved this approach to be far from ideal. The closing of the gap between grooved plates, whose teeth are smaller, drastically reduces the flow area, reduces the feed capacity, and makes the matrices prone to clogging. In addition, smaller teeth reduce the magnetic field and its gradient, leading to poor results with ultra-fine ore particles. This research proves that bigger teeth are better suited for high intensity magnetic separation of ultra-fines because they avoid matrix clogging thanks to the larger slurry flow area. Additionally, bigger teeth amplify the magnetic field “Bmax” and increases the magnetic gradient “Grad (∆B /∆X)”. The positive results of this new “BigFLUX Matrix” technology, are being displayed in several mining operations worldwide, increasing metallurgical recovery and producing high quality concentrates and low iron content sand from iron ore tailings.