Abstract RCC using hematite as an aggregate has interesting characteristics for use in massive structures or structures for radiation shielding. In Brazil, there is a considerable amount of hematite ore tailings without practical use, which makes this material an environmental problem and a matter of public safety. Thus, the search for alternatives to use these tailings is a priority environmental concern. An RCC containment dam with hematite aggregate was constructed to protect the basin of the Barao de Cocais River, including the city of Barao de Cocais in the State of Minas Gerais in Brazil, from a possible rupture of the Sul Superior tailings dam in the Congo Soco iron mine. Approximately 150,000 m3 of RCC was deposited in three months. In this article, the results of the technological control tests during the construction of the containment are presented and compared with the results of the cores extracted after the construction, showing their coherence and strength performance compared with RCC using conventional aggregate. Also, studies related to the performance of radiation shielding of this RCC are presented. An attenuation of 10% of 1.6 MeV gamma radiation in relation to conventional concrete was observed.

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).

Abstract Colorless quartz can develop a green color when submitted to gamma irradiation and its development is related to the presence of molecular water and hydroxyl groups in the quartz crystalline structure. In the present study, colorless quartz crystals hosted in geodes within rhyodacites of Serra Geral Group, Southern Brazil, were selected to test the potential development of green color. The samples were analyzed by infrared (IR) and thermogravimetric (TGA) techniques, in addition to the Amethyst Factor (fa) method. All samples showed an absorption bands in the IR, indicating possible development of a green or purple color, and fa analysis indicated the samples would develop a green color. All samples became colored after irradiation, presenting color zoning: from colorless to grayish-green, and from grayish-green to slightly purplish. Some samples showed a greenish colored zone and developed an amethyst phantom crystal in its apical portion. In addition, a high content of water in samples that remained colorless after irradiation was detected. It is here interpreted that water concentration varied during quartz crystallization, enabling the development of the green color, and that the excess of water can inhibit the development of radiation-induced color in colorless natural quartz crystals.

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.

Abstract The use of the sediment deposited in the Candonga dam after the collapse of the Fundão dam is being considered as raw material for civil construction. Blocks were obtained by adding 5 % of sodium carbonate and 13 % of water to the dried dredged sediment, which was mixed and heat treated at 700 ºC and cooled slowly inside the oven to room temperature. The water absorption of the blocks was in the 12-16 % range, the loss of mass in water was (0.01±0.01) %, the density was (1.95±0.03) g/cm3, the compression strength was (11.05±1.29) MPa (reference value ≥ 1.7 MPa), and the flexural strength was (4.42±0.69) MPa (reference value ≥ 3.5 MPa). Small cracks and pores, as well as the growth of white spots (efflorescence) were observed on the surface of the blocks, which can be avoided or attenuated by improving the compaction pressure and the heat treatment.

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.

Abstract Beryl, Be3Al2(SiO3)6, is a natural gemstone with many colors. Some of these colors can be induced or modified by exposure to ionizing radiation, by heating, and maybe by electrodiffusion. Small contents of chromophore chemical elements are related to the colors of beryl, like iron, chromium, vanadium, manganese, and others. There is great interest in relation to methods of improving or inducing colors in beryl. There is evidence that infrared spectroscopy (FTIR) can contribute to foresee beryl behavior submitted to procedures for color change. It was observed that electrodiffusion with or without contaminant ions did not alter the FTIR spectrum of aquamarines, unlike heat treatment. Green samples have a higher content of type I water molecules, whereas blue samples have a higher content of type II water molecules. Significant changes in FTIR spectra of aquamarines were observed only in green samples after exposure to gamma rays or to heat. The vanishing of the band at 3633 cm-1 may be related to the position of Na+ ion in the crystal lattice of beryl.

Abstract The oxygen-uranium (O-U) system has various oxides, such as UO2, U4O9, U3O8, and UO3. Uranium dioxide is the most important one because it is used as nuclear fuel in nuclear power plants. UO2 can have a wide stoichiometric variation due to excess or deficiency of oxygen in its crystal lattice, which can cause significant modifications of its proprieties. O/U relation determination by gravimetry cannot differentiate a stoichiometric deviation from contents of other uranium oxides in UO2. The presence of other oxides in the manufacturing of UO2 powder or sintered pellets is a critical factor. Fourier Transform Infrared Spectroscopy (FTIR) was used to identify U3O8 in samples of UO2 powder. UO2 can be identified by bands at 340 cm-1 and 470 cm-1, and U3O8 and UO3 by bands at 735 cm-1, 910 cm-1, respectively. The methodology for sample preparation for FTIR spectra acquisition is presented, as well as the calibration for quantitative measurement of U3O8 in UO2. The content of U3O8 in partially calcined samples of UO2 powder was measured by FTIR with good agreement with X-rays diffractometry (XRD).

A pedra composta é feita de uma mistura de materiais granulados ligados por uma resina polimérica. Técnicas de planejamento fatorial foram utilizadas para determinação da influência de fatores na fabricação da pedra composta. Seis fatores foram analisados: tipo de resina, uso de promotor de adesão, pressão de compactação, duração da vibração, utilização de vácuo e programa de cura. A variável de resposta foi a resistência à flexão. Foi, inicialmente, empregado um planejamento fatorial fracionário 2IV6-2 com cinco réplicas, cujo resultado indicou a influência significativa dos fatores tipo de resina, uso de promotor de adesão e programa de cura, assim como da interação entre eles e da interação entre tipo de resina e promotor de adesão. Os dados foram rearranjados num planejamento fatorial 23 completo com dez réplicas para o cálculo da influência desses efeitos. A falta de influência dos outros fatores sugere que pressões de compactação mais baixas devem ser utilizadas para a otimização do processo, com o uso da metodologia de superfície de resposta.

Composite stone is made of crushed materials bound by a polymer resin. A design of experimental techniques was used to evaluate the influence of factors (resin type, use of adhesion promoter, compaction pressure, vibration duration, use of a vacuum, and cure program) on the manufacturing of composite stone. The response variable was flexural strength. A 2IV6-2 fractional factorial design with five replications was initially used, which showed that resin type, use of adhesion promoter, and a cure program were factors of significant influence, as well as the interaction between them and the interaction between the resin type and the use of adhesion promoter. The data was re-arranged into a full 23 factorial design with ten replications to calculate the influence of these factors. The lack of influence of the other factors suggests that lower pressures should be used to improve the process by employing the surface response methodology.

A forte demanda por bens minerais verificada nas últimas décadas tem levado o setor mineral a ampliar sua capacidade produtiva. Diferentes métodos de concentração têm sido propostos para separação seletiva da apatita dos contaminantes carbonatos e silicatos presentes em minérios fosfáticos. Separação magnética, hidrogravimétrica e calcinação são métodos que apresentam baixa eficiência e custo elevado. A flotação é o método mais indicado, porém a seletividade é dificultada devido à similaridade da composição química superficial entre fosfatos e carbonatos, a alta atividade superficial dos coletores utilizados, interações entre espécies iônicas dissolvidas de um mineral sobre outro e, também, entre espécies iônicas dissolvidas e reagentes. Nesse estudo, realizado em laboratório, oito diferentes depressores, orgânicos e inorgânicos, foram testados na flotação aniônica direta de um fosfato sílico-carbonatado. O melhor desempenho foi obtido com fécula de mandioca, que exerceu boa depressão sobre a calcita e os silicatos.

A high demand for mineral resources observed in recent decades has led to an expansion in production in the mining industry. Different process alternatives have been proposed for selective separation between apatite and contaminants (carbonates and silicates) present in phosphate ores. Magnetic separation, calcination and gravity separation processes are methods that present low efficiency and high cost. Flotation is the most common process; however the selectivity is hampered by the superficial similarity of the chemical composition of phosphates and carbonates, high surface activity of the collectors used, interactions between dissolved ionic species of certain mineral with another and also interactions between dissolved ionic species and reagents. In this study, conducted in a laboratory scale, eight different depressants, organic and inorganic, were tested in the direct flotation of a Brazilian silicate-carbonate phosphate ore. The best performance in the depression of calcite and silicates was achieved with cassava starch.

A produção de materiais que apresentem alto desempenho em suas aplicações exige avanços tecnológicos e científicos. Os elevados valores de resistência à tração e módulo de elasticidade, aliados à flexibilidade, baixa densidade e alta razão de aspecto, fazem dos nanotubos de carbono excepcionais candidatos para reforçar compósitos poliméricos. Preparamos por laminação sistemas compósitos ternários à base de resina epóxi/tecidos de fibra de carbono (para os binários), acrescendo nanotubos de carbono para os sistemas ternários. Os parâmetros estequiométricos do sistema epoxídico (valor de Phr) e concentração de nanotubos de carbono empregado nos sistemas compósitos tiveram avaliadas suas morfologias (MEV), propriedades térmicas (TG) e mecânicas (ASTM D790). Embora o sistema epoxídico com Phr 10,0 tenha apresentado uma maior estabilidade térmica, os compósitos ternários produzidos a partir do sistema com Phr 26,6 mostraram valores de tensão máxima e módulo de elasticidade até 8 vezes maiores que aqueles produzidos com o sistema Phr 10. A adição de nanotubos de carbono aos compósitos com Phr 26,6 resultou em ganhos adicionais de aproximadamente 38 e 15% na tensão máxima e no módulo de elasticidade, respectivamente. Esses resultados revelaram a limitação nos métodos de integralização de nanoestruturas a sistemas compósitos, onde as dispersões estão limitadas a uma série de fatores inerentes a interação química e/ou física durante a fabricação dos compósitos nanoestruturados.

The production of materials that exhibit high performance in their applications requires scientific and technological advances. The high values of tensile strength and modulus of elasticity, combined with flexibility, low density and high aspect ratio, make carbon nanotubes exceptional candidates for reinforced polymer composites. We prepared by lamination composite systems based on epoxy resin/woven carbon fiber (for binary), plus carbon nanotubes for the ternary systems. The effect of the stoichiometry of the epoxy system (Phr value) and concentration of carbon nanotubes used in the composite systems was evaluated by their morphological (SEM), thermal (TG) and mechanical properties (ASTM D790-10). Although the epoxy system with 10.0 Phr has presented a higher thermal stability, the ternary composite system produced with 26.6 Phr showed values of maximum stress and elastic modulus up to 8 times greater than those produced with the 10 Phr system. The addition of carbon nanotubes to composites with 26.6 Phr resulted in additional increase of approximately 38 and 15% of the maximum stress and elastic modulus, respectively. These results revealed a limitation in the methods of incorporation of the nanostructures in composite systems, where the dispersion is limited by a number of factors, inherent to the chemical and/or physical interactions during fabrication of nanostructured composites.

Glass-ceramic materials made of 40.0 wt. (%) of sandy tailing from banded iron formation exploitation and 60 wt. (%) of slag from steelwork were analyzed. Vitrification was obtained by heating the batch samples up to 1400 °C for 1 hour and quenching the melt on a stainless steel plate. Devitrification was obtained by heat-treating the as-quenched glass samples in isothermal conditions at 750 and 1000 °C for 2 hours. FTIR spectroscopy analysis on the devitrified samples indicates a peak shift towards higher wave number with respect to the as-quenched glass because of the crystallization. XRD analysis revealed the presence of crystalline diopside CaMgSi2O6 as the major phase in the glass samples isothermally heat-treated at 1000 °C. Results also indicated that the devitrification at 1000 °C and an incipient devitrification at 750 °C resulted into harder glass-ceramic materials.

Apesar da grande produção de quartzo em Minas Gerais, pouco é conhecido sobre a influência do ambiente geológico na geração das variedades coloridas através de tratamento. Sabe-se que a irradiação gama, seguida ou não de aquecimento, conduz à formação de cores, tais como acontece com a ametista, prasiolita, green gold, beer, cognac, whisky e champagne. Amostras de ambientes hidrotermal e pegmatítico foram submetidas a ensaios por espectroscopia de absorção na região do infravermelho por transformada de Fourier (FTIR) e irradiação gama seguida ou não de tratamento térmico. Os espectros obtidos por FTIR mostram bandas correlacionadas a elementos dopantes, os quais indicam o potencial da amostra pelo aparecimento de cor e permitem determinar as doses que serão aplicadas na irradiação gama e as temperaturas que serão utilizadas no tratamento térmico. Os resultados dos ensaios mostraram que quartzo de ambiente hidrotermal com valores anômalos de ferro, com banda FTIR a 3.585cm-1, fator fa > 3,3 e área entre 400 e 600u.a*cm-1, poderá desenvolver a cor violeta; quartzo com anomalias de lítio na estrutura do cristal derivado de núcleo de pegmatitos altamente diferenciados ricos em minerais de lítio apresentando banda FTIR a 3.485cm-1, fator fLi > 2,0 e irradiado com doses de 65 a 400kGy pode desenvolver cores amarelo-esverdeadas a acastanhadas. É possível concluir que ametista e prasiolita são produzidas de quartzo de ambiente hidrotermal, enquanto variedades gemológicas raras, tais como green gold, beer, cognac, whisky e champagne são produzidas de quartzo de pegmatitos altamente diferenciados, que contêm minerais de lítio.

Despite the large production of quartz in Minas Gerais, little is known about the geological environment influence on the generation of colored varieties by treatment. It is known that gamma irradiation, followed or not by heating, leads to the generation of colors such as amethyst, prasiolite, green gold, beer, cognac, whisky and champagne. Samples from hydrothermal and pegmatitic environments were subjected to tests by absorption spectrometry in the infrared region with the FOURIER transform (FTIR), gamma irradiation and heat treatment. The obtained FTIR-spectra show characteristic bands correlated to doping-elements, which indicates the color appearance potential of the sample, and allow to quantify the applied doses of gamma irradiation and the temperatures in heat treatment. The results of the tests indicate that quartz from a hydrothermal environment with anomalous levels of iron, with FTIR-band of 3585cm-1, factor fa > 3.3 and area between 400 a 600u.a*cm-1, may develop a violet color; quartz with lithium anomaly in the crystal structure derived from nuclei of highly differentiated pegmatites rich in lithium minerals, presenting FTIR-band of 3485cm-1, fLi factor > 2 and irradiated with doses of 65 to 400kGy, may develop yellow-green and brown colors. It is possible to conclude that amethyst and prasiolite are produced from quartz from a hydrothermal environment, while rare varieties such as green gold, beer, cognac, whisky and champagne are generated from quartz from highly differentiated pegmatites that bear Li-minerals.

The infrared bands of amethyst and prasiolite samples from different origins were correlated to the trace elements contents. Amethysts have an iron content greater than 20 ppm and a low content of sodium and potassium. Prasiolites have an aluminum content greater than 120 ppm and a higher overall trace elements content, which accounts for a strong absorption between 3200 and 3600 cm-1. Colorless samples of quartz that become amethysts and prasiolites after irradiation have infrared spectra at room temperature with a broad band at 3441 cm-1 and a sharp band at 3595 cm-1. The broad band splits in several bands at low temperatures that are related to AlSi and FeSi. The color of amethysts and prasiolites are assigned to [AlSiO4/h+]º and [FeSiO4/h+]º centers formed by the exposure to ionizing irradiation and to the influence of lattice distortions due to the content of iron as a substitute for silicon and a high content of trace elements of large ionic radius like potassium.

Porous ceramic materials based on calcium phosphate compounds (CPC) have been studied aiming at different biomedical applications such as implants, drug delivery systems and radioactive sources for brachytherapy. Two kinds of hydroxyapatite (HAp) powders and their ceramic bodies were characterized by a combination of different techniques (XRF, BET method, SEM, ICP/AES and neutron activation analysis - NAA) to evaluate their physico-chemical and microstructural characteristics in terms of chemical composition, segregated phases, microstructure, porosity, chemical and thermal stability, biodegradation and incorporation of substances in their structures. The results revealed that these systems presented potential for use as porous biodegradable radioactive sources able to be loaded with a wide range of radionuclides for cancer treatment by the brachytherapy technique.