323 research outputs found

    Pyrite utilization in the carboniferous region of Santa Catarina, Brazil : potentials, challenges, and environmental advantages

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    The main coal seams explored in the coal region of Santa Catarina are Barro Branco (BB) and Bonito (BO). Owing to the association with the mineral matter, the tailings generated in the beneficiation are arranged in disposal areas, and subject to the generation of acid mine drainage (AMD). The objective of this study was to evaluate the use of pyrite present in the coal rejects of the BB and BO seams and the environmental gains with desulfurization. For this purpose, densimetric separability test, ash, sulfur, and AMD generation analyses were performed. In addition, the amount of pyritic concentrates and sulfuric acid were estimated considering the current level of production. Three densimetric fractions were obtained: less than 2.2 (energetic material), between 2.2 and 2.7 (low sulfur material), and greater than 2.7 g cm-3 (pyrite concentrate). The results revealed that the two seams could be beneficiated by gravimetric processes, obtaining pyrite concentrates with approximately 60% pyrite. By converting pyrite to sulfuric acid would represent an increase of 500,000 tons per year in the Brazilian production of this material and, in environmental terms, a reduction of up to 90% of the acidity potential to be disposed in the environment in the case of the BB seam and 65% for the BO seam. It was also observed that the “desulfurized” fraction of the BO had higher levels of pyrite and a higher potential for acidity generation than the BB seam, implying greater risks of environmental contamination and higher acid water treatment costs

    Quantum probing of null-singularities

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    We adapt the dual-null foliation to the functional Schr\"odinger representation of quantum field theory and study the behavior of quantum probes in plane-wave space-times near the null-singularity. A comparison between the Einstein-Rosen and the Brinkmann patch, where the latter extends beyond the first, shows a seeming tension that can be resolved by comparing the configuration spaces. Our analysis concludes that Einstein-Rosen space-times support exclusively configurations with non-empty gravitational memory that are focussed to a set of measure zero in the focal plane with respect to a Brinkmann observer. To conclude, we provide a rough framework to estimate the qualitative influence of back-reactions on these results.Comment: 12 pages, 3 figures, journal version, typos correcte

    Hydrometallurgical processing of Brazilian iron ore tailings for the synthesis of pigments

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    The aim of this study was to investigate the synthesis of iron oxide pigments from IOT. The sample of IOT was obtained through mining activity of the Quadrilátero Ferrífero in the state of Minas Gerais, Brazil. The procedure was carried out by hot acid leaching with hydrochloric acid (HCl) which allowed the recovery of about 95% of the iron in a liquor. The iron-based pigments— red (IBP_R), black (IBP_B), and yellow (IBP_Y)—were synthetised from the liquor by selective precipitation, crystallisation, and thermal procedures. The pigments were characterised by particle size distribution, mineral and chemical compositions, as well as colourimetric properties. The process of synthesis was successful and the procedure was shown to maximise the utilisation of mineral resources and minimise the environmental, social, and economic impacts associated with IOT disposal

    Heterogeneous photocatalytic degradation of dyes in water/alcohol solution used by the brazilian agate industry

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    The agate dyeing industry has been commonly seen as a high-pollution industry. Dyeing wastewater treatment is considered one of the most important categories for water-pollution control, because of its intense colour and the high concentration of organic contaminants. Most dyes used in the process present minimal biodegradability due to aromatic organic compounds in their structure. Using a photocatalytic reactor, experiments were carried out to study the decolorization of a water solution containing 8% ethylic alcohol and 200 mg L−1 of the dye Rhodamine B (RhB), the most difficult colorant to degrade among the used by the agate industry. The best conditions were further applied to treat the same agate water/ethyl alcohol solution containing a mixture of 200 mg L−1 of Rhodamine B (RhB), Crystal Violet (CV), Brilliant Green (BG), and Blood Red (BR). All the experiments were performed in a 2 L reactor equipped with ultraviolet (UV) lamps, at a wavelength of 365 nm, with powdered TiO2 or ZnO as the catalyst. The results indicated that the optimal decolorization conditions were attained with 2.5 g L−1 of the catalyst at pH 10 and an irradiation time of 80 min. The process resulted in complete degradation of CV, BG and 80% - 90% degradation of RhB and BR. The catalyst ZnO presented a performance somewhat better than TiO2. It is possible to conclude that the process of heterogeneous photocatalysis is effective for decolorization of water streams from the agate industry

    Using static, kinetic and metal mobility procedures to evaluate possibilities of coal waste land disposal at Moatize Mine, Mozambique

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    Coal mine waste rocks produced during mining and beneficiation can affect the environment due to land degradation and acid mine drainage generation. However, proper characterization and treatment of mineral processing wastes creates options for safe disposal, enhancing the environmental performance. The aim of this study was to use static and kinetic tests to assess properties of coal waste produced at the Moatize Mine in Mozambique, one of the largest "world-class" coal deposits. The study included sampling and characterization of coarse and fine wastes generated during coal beneficiation. Both materials were analyzed in terms of granular properties, static procedures - immediate composition, sulfur forms, mineralogical composition, elemental composition, acid-base balance – and kinetic behavior in humidity cell tests. The conjugation of these techniques indicates that these wastes have a low water acidification potential and low geochemical mobility of toxic elements. Therefore, it was concluded that fine and coarse wastes could be used in land shaping procedures

    Removal of pollutants from an AMD from a coal mine by neutralization/precipitation followed by “in vivo” biosorption step with the microalgae Scenedesmus sp.

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    This work evaluates the benefits of a complementary treatment step of acid mine drainage (AMD) using the algae Scenedesmus sp. in terms of algae biomass production, residual metal removal, and the toxicity of the discharged water. Conventional treatment by neutralization/precipitation of an AMD from a coal mine in Brazil was conducted with Ca(OH)2 at pH 8.7. Algal growth studies were performed in the treated AMD, with and without a nutrient supply. The raw e uent and treatments were compared in terms of residual concentration of metals and sulfate, conductivity, and toxicity with the Allium cepa and Daphnia magna test organisms. The results show that the conventional treatment allowed a major metal removal, reduction in the conductivity, and good indices in the toxicological parameters evaluated. The biosorption with in vivo microalgae improved the quality of the e uent for residual metals. No significant toxicity was observed to Allium cepa in all treatments performed, while the Daphnia magna test indicated a reduction in toxicity after the biosorption step. It was concluded that algae growth can be carried out in treated mine waters, providing algae biomass and helping to achieve the standards for water discharge