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[en] Coal mining wastes are associated with serious environmental problems; they have potential as building materials, including alkali-activated cement. In this study, the effect of different coal mining wastes on the mechanical properties and microstructural development of alkali-activated materials (AAMs) was evaluated through XRD, SEM and FTIR spectroscopy. Different alkali-activated compounds were produced; the alkaline solution was composed of NaOH+Na2SiO3. The results obtained using the calcined coal sludge showed excellent mechanical performance, with compressive strength higher than 60 MPa. However, addition of metakaolin and ordinary Portland cement was necessary to increase the mechanical performance of calcined coal gangue materials. The formation of N-A-S-H gel and the incorporation of iron ions into the cementitious matrix were evidenced. Ultrasonic pulse velocity indicated the early polymerization during the reaction processes. The study verified that the different characteristics of the wastes influence the performance of alkali-activated materials.
[es]Los residuos de minería de carbón causan serios problemas ambientales, no obstante, tienen potencial como material de construcción, destacándose los cementos activados alcalinamente. El efecto de los residuos de carbón sobre las propiedades mecánicas y el desarrollo microestructural de los cementos activados alcalinamente son objeto de este estudio. Para ello, se utilizaron las técnicas de DRX, SEM y FTIR. Se produjeron diferentes compuestos activados alcalinamente, utilizando NaOH + Na2SiO3 como activador alcalino y curado térmico (50 °C durante 24 h). Los resultados obtenidos a partir del lodo de carbón calcinado mostraron un excelente rendimiento mecánico, con una resistencia a la compresión superior a 60 MPa. Sin embargo, en el caso de los materiales obtenidos a partir de la ganga de carbón calcinada, fue necesaria la adición de metacaolín y cemento Portland para aumentar sus resistencias mecánicas. Asimismo, se evidenció la formación de gel N-A-S-H y la incorporación de iones de hierro en la matriz cementante. El ensayo de velocidad de pulso ultrasónica indicó la polimerización inicial durante el proceso de reacción. Gracias a este se ha comprobado que las diferentes características de los residuos influyen en las propiedades y comportamiento de los correspondientes materiales activados alcalinamente.
[en] Lake Qinghai in the Qinghai-Tibet plateau is the largest lake in China. This study firstly reported the geochemistry of Cd in the lake. Water samples were collected from Lake Qinghai (n = 69) and Buha River (n = 12), while sediment (n = 22) and topsoil (n = 45) samples were collected from the lake and around the lake area, respectively. In addition, pore water samples (n = 20) were separated from sediment samples. Water samples were analyzed for pH, K, Na, Ca, Mg, Cl, S, and Cd, while sediment and topsoil samples were analyzed for K, Na, Ca, Mg, Al, Fe, Mn, S, Sc, and Cd. The average concentration of Cd was 0.014 μg L−1 in the water of Lake Qinghai and 0.007 μg L−1 in the water of Buha River. However, the average concentration of Cd was 0.320 μg L−1 in the sediment pore water, much higher than that in the lake water and river water. Cadmium concentration in the lake water might be mainly controlled by salinity, while it in the pore water might be mainly controlled by carbonate minerals. Cadmium concentration in the river water might be controlled by alkalinity and pH. The average concentration of Cd in the sediment was 0.284 mg kg−1. The enrichment of Cd in the lake sediment was significantly higher than that in the topsoil around the lake. Anthropogenic atmospheric deposition of Cd did not led to the increase in dissolved Cd level in the lake water, but led to its enrichment in the lake sediment.
[en] This study evaluated the effect of the application of liquid aerobic treated manure (continuous liquid composting, CLC) on physical, chemical and biological soil properties, with the objective of monitoring changes induced by soil management with CLC as a biofertilizer. Colonia, Uruguay (lat. 34,338164 S, long. 57,222630 W). Soil’s chemical properties, including nitrogen mineralization potential (NMP) and 15 microbiological properties (microbial biomass carbon, MBC; mesophylic aerobic bacteria; actinobacteria; filamentus fungi; fluorescein diacetate hydrolysis; dehydrogenase; with NMP; acid and alkaline phosphatase; cellulolose degraders; P-solubilizing bacteria; nitrifying; denitrifying and free-living N-fixing microorganisms; glomalin; and soil-pathogenicity index, SPI) were evaluated in two sites with similar cropping history, with one and three years of respective CLC application. CLC application had significant effects on soil microbial biomass (p<0.05), soil enzyme (p<0.1) and functional groups activity (p<0.05). SPI decreased in both sites with CLC application. No significant variations were detected for the chemical variables, with the exception of NMP, which was significantly high (p<0.05) in soil treated with CLC at both sites. The improved biological soil properties analyzed (MBC, soil enzyme activities and SPI, together with NMP) emerged as reasonable indicators to assess and monitor the effects of CLC application.
[en] The conference is dedicated to the very actual problem of nuclear energy production and chemical technology, which has been in the spotlight of the world scientific community for many years - radiation and chemical safety. It is hope that the result of this Conference will be an important stage in the history of science in the area of Radiation Chemical Safety.
[en] Starting from the Breit–Wigner model, we present a generalized approach for calculating the electrical conductance of a one-atom metallic constriction with electrochemical-potential control. In addition, the corresponding current intensity is determined. On the one hand, the nanoconstriction is conceived as a dilute (degenerate) Fermi gas (relatively low electron concentrations are considered) and, on the other hand, non-dilute gas is considered. Under these conditions, the Fermi energy-level into the Breit–Wigner formula is replaced by the corresponding chemical-potential energy. We emphasize the role of the optical potential as significant ingredient of the chemical potential.
[en] Microfluidic-based cell handling techniques have become promising tools for biochemical applications, and many such techniques have been developed with the advancement of microfabrication technologies. A microfluidic-based platform used for biochemical analysis offers numerous benefits, including small sample consumption, massive parallelization, rapid analysis, and the capability for single-cell analysis, which are difficult to achieve in conventional cell handling methods on a large scale. It also exhibits precise spatial and temporal control of the local cellular microenvironments based on microfluidic networks in accordance to the unique fluidic phenomena of microfluidics. This review focuses on various cell handling methods that take advantage of microfluidics by classifying them in accordance to specific functions required for biochemical analyses, including (i) cell transfer, (ii) cell separation and sorting, (iii) cell immobilization, (iv) cell isolation and encapsulation, and (v) cell retrieval. (topical review)
[en] A steady magnetic field (SMF) was imposed during solidification of pure Mg. The effects of SMF on structure and bio-corrosion behavior of pure Mg were investigated. Results show that no detectable difference can be discerned with regard to the influence of SMF on the macrostructure of pure Mg. The (0002) basal plane replaced the () pyramidal plane as the primary plane with SMF treatment. The (0002) plane was further intensified with the increase of magnetic field intensity, while the relative intensity of the () plane became lower and lower. Immersion testing and electrochemical measurements have indicated that the beneficial effect of SMF treatment on the bio-corrosion resistance of pure Mg. The bio-corrosion resistance of pure Mg was further increased as magnetic field intensity increased. (paper)
[en] This paper reports on the results of radiation monitoring of bottom sediments in Yenisei Gulf for the period from 1995 to 2016. Clear positive trends in changing the radiation situation have been established. The obtained results showed that the radiocesium activity decreased by half not only in the surface layer but also in different horizons within the bottom sediments. The avalanche sedimentation rates ranging from 3.2 to 5.9 mm per year were determined. To estimate the sedimentation rates in the geochemical barrier zone, an alternate technique was proposed.
[en] Highlights: • Very high-order spatial discretisations in electrochemical simulations are tested. • Asymmetric 4-to7-point approximations enable to use grids with less than 15 points. • Brute force resolution of the resulting problem is competitive in all cases studied. • Comparison between LU and QR decompositions and sparse matrix methods is performed. • Easy-to-implement, C++ example programs are provided. The use of very high order spatial discretisation in digital simulation of electrochemical experiments is assessed, considering up to asymmetric 8-point approximations for the derivatives. A wide range of conditions are examined, including several mechanisms and electrodes and potential-step and potential-sweep experiments. In all cases it is found that asymmetric multi-point approximations in combination with exponentially expanding grids provides very accurate results and with very reduced number of grid points (<15). Consequently, the direct (‘brute force’) resolution of the finite-difference equation system by standard matrix techniques becomes a competitive and more general alternative to specialised methods like the Thomas algorithm.
[en] The Escuela Centroamericana de Geologia in conjunction with the, Laboratorio Nacional de Materiales and Modelos Estructurales both of the Universidad de Costa Rica, have carried out qualitative studies on the effects of acid rock drainage (DAR) in the materials used for stabilization and erosion control. on the slopes (km 38 + 600, km 45 + 000, km 47 + 000 and km 48 + 000) on national route No. 27 (RN-27). The present study developed a methodology to recreate and measure the impact that acid drainage has on the rock mass and on the cast concrete of the slopes, through experiments in the laboratory and in the field. The Instituto Costarricense de Electricidad has also carried out an analysis on the effect of acidic waters on concrete. This study is the first in the country focused on highway slopes, which use shotcrete for stabilization. Acid drainage is acidified waters as a consequence of the oxidation of minerals rich in sulfur. These waters, when draining between the materials of the slope, cause physical and mineralogical changes in their original composition and can cause instability. The importance of this study lies in the contribution of a methodology for future work on materials exposed to similar conditions in other national routes and for the support of decision-making corresponding to the stabilization of slopes affected by this process. The hypothesis raised indicates that if the healthy rocks that emerge in the vicinity of the RN-27 and the shotcrete designed and projected with the same acidic specifications that simulate the DAR, then there will be changes in their original characteristics. But if the material used does not have a calcareous component, it will not react with the acid and no changes will be made. This hypothesis was fulfilled and thus from this study, there is enough evidence to justify not using the concrete shot in place where the DAR is given. Five different tests were carried out, three in the laboratory and two in the field, with samples of volcanic breccia, andesite and shotcrete, of which the first two were obtained in the field and the last one was built with the same mixing design as the one placed on site. Changes in mass, dimensions and mineralogical characteristics were analyzed by optical microscopy and X-ray scattering. The results showed that samples exposed to a high level of acidity (pH ≤ 2), have a greater impact on their characteristics, than those that are in contact with a solution of lower acidity (2.0 ≤ pH ≤ 5.5). Shotcrete is the most susceptible material, of all those tested, to attack by acid dissolution, generating gypsum and ettringite as a mineralogical product of the reaction. The volcanic breccia samples are affected only by the dissolution of carbonates in the clasts and veinlets, and the andesite, lacking a calceous component in its composition, did not show alterations in the laboratory. Of the physical properties considered and analyzed, the mass presented the most significant changes while the dimensions did not reflect considerable changes. It was demonstrated, both in the field and in the laboratory, that the exposure of the shotcrete to acid solutions generated changes in its physical and mineralogical properties at the macro and microscopic level. This implies the deterioration in the quality of the concrete and explains the problems of stability and collapse of this material in the RN-27. According to the results in the laboratory and in the field, the accelerated experiment is validated in the laboratory and the working hypothesis is verified. (author)
[es]La Escuela Centroamericana de Geologia en conjunto con el Laboratorio Nacional de Materiales y Modelos Estructurales ambos de la Universidad de Costa Rica, han realizado trabajos cualitativos sobre los efectos de drenaje acido de roca (DAR) en los materiales utilizados para la estabilizacion y control de erosion en los taludes (km 38+600, km 45+000, km 47+000 y el km 48+000) en la ruta nacional No. 27 (RN-27). El presente estudio desarrollo una metodologia para recrear y medir el impacto que tiene el drenaje acido en el macizo rocoso y en el concreto de tipo lanzado de los taludes, mediante experimentos en el laboratorio y en campo. El Instituto Costarricense de Electricidad, ha realizado tambien analisis sobre el efecto de las aguas acidas en el concreto, este estudio es el primero en el pais enfocado en taludes de carretera, que utilizan concreto lanzado para su estabilizacion. El drenaje acido son aguas acidificadas consecuencia de la oxidacion de minerales ricos en azufre. Estas aguas al escurrir entre los materiales del talud, provocan cambios fisicos y mineralogicos en la composicion original de estos y pueden ocasionar inestabilidad. La importancia de este estudio esta en el aporte de una metodologia para futuros trabajos sobre materiales expuestos a condiciones similares en otras rutas nacionales y para el apoyo de la toma de decisiones correspondientes a la estabilizacion de taludes afectados por este proceso. La hipotesis planteada indica que si las rocas sanas que afloran en las inmediaciones de la RN-27 y el concreto lanzado disenado y proyectado con las mismas especificaciones del que fue colocado en los taludes, son expuestas a disoluciones acidas que simulan el DAR, entonces se daran cambios en sus caracteristicas originales. Pero si el material utilizado no tiene componente calcareo este no reaccionara con el acido y no se procuciran cambios. Esta hipotesis si se cumplio y asi a partir de este estudio, existen suficientes evidencias que justifiquen no utilizar el concreto lanzado en sitios donde se da el DAR. Se realizaron cinco ensayos diferentes, tres en laboratorio y dos en campo, con muestras de brecha volcanica, andesita y concreto lanzado, de las cuales las dos primaras fueron obtenidas en campo y el ultimo fue construido con el mismo diseno de mezcla del colocado en el sitio. Se analizaron los cambios de la masa, dimensiones y las caracteristicas mineralogicas mediante microscopia optica y dispersion de rayos X. Los resultados evidenciaron que las muestras expuestas a un algo nivel de acidez (pH ≤ 2), tienen un mayor impacto en sus caracteristicas, que las que estan en contacto con una disolucion de menor acidez (2,0 ≤ pH ≤ 5,5). El concreto lanzado es el material mas susceptible, de todos los ensayados, al ataque de la disolucion acida generando como producto mineralogico de la reaccion, yeso y etringita. Las muestras de brecha volcanica se ven afectadas solamente por la disolucion de los carbonatos en los clastos y vetillas, y la andesita al carecer de componente calcareo en su composicion, no evidencio alteraciones en el laboratorio. De las propiedades fisicas consideradas y analizadas, la masa presento los cambios mas significativos mientras que en las dimensiones no se reflejaron cambios considerables. Se demostro, tanto en campo como en el laboratorio, a que la exposicion del concreto lanzado disoluciones acidas genero cambios en sus propiedades fisicas y mineralogicas a nivel macro y microscopico. Esto implica el deterioro en la calidad del concreto y explica los problemas de estabilidad y colapso de esta material en la RN-27. De acuerdo con los resultados en laboratorio y en campo, se valida el experimento acelerado en laboratorio y se comprueba la hipotesis de trabajo. (autor)