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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] Acid mine drainage often results from the oxidation sulfide minerals to form sulfuric acid. As a consequence, high concentrations of metals in the both the suspended and dissolved state result from the low pH water. This paper discusses several of the more common treatment methods for acid mine drainage including the use of chemical precipitation agents, pH correction agents, filtration methods, and biodegradation methods. Advanced treatment technologies are also briefly described and include microfiltration, reverse osmosis, ion exchange, and electrodialysis
[en] The purpose of this work was to augment the alkaline protease production from Bacillus subtilis by using chemical mutagen (MMS) and UV mutagenesis. A number of mutants were isolated which produce high levels of extra cellular proteases. Analysis of culture supernatants of these mutants had shown that the total amounts of proteolysis activity were increased from 1 to 2 fold over the wild strain. Clones showing promote response were further characterized by analyzing different parameters; like of Temperature, pH substrate concentration and incubation period, to study the activity of protease enzyme. (author)
[en] Simple mass balance equations (SMBE) of critical acid loads (CAL) in forest soil were developed to assess potential risks of air pollutants to ecosystems. However, to apply SMBE reliably at large scales, SMBE must be tested for adequacy and uncertainty. Our goal was to provide a detailed analysis of uncertainty in SMBE so that sound strategies for scaling up CAL estimates to the national scale could be developed. Specifically, we wanted to quantify CAL uncertainty under natural variability in 17 model parameters, and determine their relative contributions in predicting CAL. Results indicated that uncertainty in CAL came primarily from components of base cation weathering (BCw; 49%) and acid neutralizing capacity (46%), whereas the most critical parameters were BCw base rate (62%), soil depth (20%), and soil temperature (11%). Thus, improvements in estimates of these factors are crucial to reducing uncertainty and successfully scaling up SMBE for national assessments of CAL. - A comprehensive uncertainty analysis, with advanced techniques and full list and full value ranges of all individual parameters, was used to examine a simple mass balance model and address questions of error partition and uncertainty reduction in critical acid load estimates that were not fully answered by previous studies
[en] This paper concerns an experimental study of the influence of short glass-fibres randomly oriented of a reinforced cement-based composite on the mechanical behaviour. The matrix material parameters used are: cement/sand ratio and water/cement ratio fixed at 0.5; the glass-fibre content (0%, 0.5%, 1.0%, 1.5%, 2% and 2.5%) and fibre lengths (3, 6 and 12 mm). Composites mechanical characterisation under static behaviour at flexural and compression tests, shows that the reinforcement effect is beneficial only in flexural case. A synergy (matrix-reinforcement) was observed when fibre length of 12 mm is used with application rate of 2% in flexural. The fatigue behaviour determined by Wöhler plots (stress-number of cycles to rupture), derived from experimental results; showed a large results dispersion which is attributed to many causes initiating this damage. The cyclic tests illustrate brittle character of these materials; even with low-amplitude cycles of loading no adaptation of these materials can be reported.
[es]Este trabajo aborda el estudio experimental de la influencia de fibras de vidrio cortas orientadas al azar sobre el comportamiento mecánico de un composite reforzado de base cemento. Los parámetros de la matriz utilizados son: relación cemento/arena y relación agua/cemento fijada en 0,5; el contenido de fibra de vidrio (0%, 0,5%, 1,0%,1,5%, 2% y 2,5%) y longitudes de fibra (3, 6 y 12 mm). Los resultados mecánicos de estos compuestos bajo comportamiento estático (flexión y compresión), muestran que el efecto de refuerzo es beneficioso unicamente a flexión. Se observó una sinergia (refuerzo de la matriz) cuando se usó la fibra de 12 mm con una tasa de aplicación del 2% en flexión. El comportamiento a fatiga determinado por las curvas de Wöhler (número de ciclos hasta la rotura), derivado de los resultados experimentales; mostró una gran dispersión de resultados que se atribuye a las muchas causas que pueden iniciar este daño. Las pruebas cíclicas ilustran el carácter quebradizo de estos materiales y no se puede indicar que exista adaptación de estos materiales, incluso con ciclos de carga de baja amplitud.
[en] Acid rain is real; the pH of precipitation in many areas of the world is below its normal equilibrium value, and concentrations of inorganic N and S are elevated above background. The impact of acid rain on soil microbial processes is less clear. This is largely because of the chemical buffering of the soil ecosystem and the inherent resiliency and redundancy of soil microorganisms. Microorganisms have an amazing capacity to adapt to new situations, which is enhanced by their ability to evolve under selection pressure. Their resilience is a function of both the large number of microorganisms present in a given volume of soil and their high growth rate relative to macroorganisms. This suggests that microorganisms are likely to be able to adapt more quickly to acidification than plants or animals, which may be one reason why symbiotic associations, such as ectomycorrhizae, are more susceptible to acid inputs than their saprophytic counterparts
[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] A short-term study was done to analyze the state of acidification of surface water at Semenyih Dam. This study is part of a continuous monitoring programme for Malaysia as a participatory country of EANET (Acid Monitoring Network in East Asia). Surface water samples were taken at selected points of the dam from February to December 2005. Temperature, electrical conductivity, pH, alkalinity, acid neutralizing capacity (ANC) as well as concentration of specific ionic species were measured, determined and analysed in this study. Present available sort-term study data indicates Semenyih Dam surface water is currently not undergoing acidification. (author)
[en] Enhanced reductive dehalogenation is an attractive treatment technology for in situ remediation of chlorinated solvent DNAPL source areas. Reductive dehalogenation is an acid-forming process with hydrochloric acid and also organic acids from fermentation of the electron donors typically building up in the source zone during remediation. This can lead to groundwater acidification thereby inhibiting the activity of dehalogenating microorganisms. Where the soils' natural buffering capacity is likely to be exceeded, the addition of an external source of alkalinity is needed to ensure sustained dehalogenation. To assist in the design of bioremediation systems, an abiotic geochemical model was developed to provide insight into the processes influencing the groundwater acidity as dehalogenation proceeds, and to predict the amount of bicarbonate required to maintain the pH at a suitable level for dehalogenating bacteria (i.e., > 6.5). The model accounts for the amount of chlorinated solvent degraded, site water chemistry, electron donor, alternative terminal electron-accepting processes, gas release and soil mineralogy. While calcite and iron oxides were shown to be the key minerals influencing the soil's buffering capacity, for the extensive dehalogenation likely to occur in a DNAPL source zone, significant bicarbonate addition may be necessary even in soils that are naturally well buffered. Results indicated that the bicarbonate requirement strongly depends on the electron donor used and availability of competing electron acceptors (e.g., sulfate, iron (III)). Based on understanding gained from this model, a simplified model was developed for calculating a preliminary design estimate of the bicarbonate addition required to control the pH for user-specified operating conditions.
[en] Chemical weathering of soils/minerals is an important process which controls the long-term neutralization of acid rain as well as the quality of surface water, ground water, and oceans. Few laboratory studies have been conducted to evaluate the response of real whole soils or soil fractions to acidification. In this research experiments were performed in a laboratory semi-continuous pH-stat reactor over the pH range 2.7 to 4.7 using Band C-horizon soil fractions from the Bear Brook Watershed, Maine, and in presence/absence of 1 to 20 mmol/L oxalate ligand in the bulk solution. Acid consumption rate and the corresponding release rates of sodium, calcium, magnesium, aluminum, iron, and silica were monitored in the laboratory reactor. Both H+-ion and oxalate promoted weathering rates were fractional order based on the concentration in bulk solution. The mixed kinetic model for the soils is: WRT = WRH + WRox = KH (H+)m + Kox [OX TD]p, where m and p are fractional orders. The hydrogen ion consumption rates were approximately equal to cation release rates on an equivalent basis for hydrogen ion promoted weathering situations where secondary precipitation was unlikely (pH < 4.7) as well as for weathering of C-horizon light fraction at pH 4.0 and oxalate concentration 1 and 5 mmol/L. The relative proportions of released species were in the neighborhood of stoichiometric ratios of bulk soil chemistry for weatherable minerals in Band C-horizon soil fractions. The experimental ratios of H/Si, Al/Si, Fe/Si, Ca/Si, Na/Si, and Mg/Si for linear weathering rates of Band C-horizon soil fractions were fairly constant in the presence and absence of oxalate ligand and strongly suggested that silica may be used as a tracer for primary mineral weathering assuming quartz is inert