1,720,967 research outputs found
Experimental evaluation of PM emission from red mud basins exposed to wind erosion
Full text linkThe disposal of industrial and mineral processing residues represents a major concern for human health and the environment as a whole. In order to reduce the impact on soil and groundwater due to the waste leachability, the implementation of environmental regulations worldwide has favored the conversion of the disposal techniques from wet to dry (i.e., dry stacking or dry disposal). Such a change in the storage practice may cause the increase of particulate matter (PM) emission from the dry surfaces of the tailings exposed to wind erosion. Considering the significance of the environmental issue on a global scale and the increasingly stricter orientation of environmental policies, the need for modeling tools capable of estimating the contribution of tailing basins to air pollution becomes apparent. The paper deals with the disposal of red mud resulting from the bauxite processing in the alumina industry. An experimental research was carried with an environmental wind tunnel to estimate the Emission Factor (EF) of the basin surfaces as a function of the main affecting variables (i.e., residue water content and wind velocity). The article reports the results of the experimental test carried out on the red mud from a major basin located in Sardinia (Italy)
Effect of the Rock Stress on the Water Jet Cutting Performance
Full text linkUnderground quarrying is rarely adopted for granite extraction due to the difficulties in the implementation of traditional technologies (drilling and explosive). As alternative to drilling and explosive, the combination of diamond wire and water jet seems to be the most promising available technology. The cutting performance achievable with the water jet technology depends on the operative parameters, the material characteristics and the state of stress within the rock massif. To assess the effect of the state of stress on the cutting rate, laboratory tests have been performed with an oscillating water jet machine on granite samples subjected to a static load. The stress distribution in the layer of rock to be removed has been evaluated by numerical simulation with the FLAC code (Fast Lagrangian Analysis of Continua). The correlation between the results of the cutting tests and the numerical models of the rock samples has been inferred. Starting from a conceptual model, which theoretically describes the relationship between the cutting rate and the stress, a step function was defined that indicates the ranges of stress where predefined values of the cutting rate are workable
Mitigation of fugitive dust impact arising from BR dry disposal
Full text linkThe development of international policies about environmental defense has enforced some major modifications in the management of industrial tailings. As regards the disposal of the residue deriving from the bauxite processing (BR) in the alumina industry, national and international regulations have encouraged the evolution from wet to dry disposal techniques. However, such a change in the storage practices poses a major concern due to the potential increase of the atmospheric impact in the surrounding areas, due to the emissions of Particulate Matter (PM) generated both by the BR disposal activities and by the wind erosion over the dried surfaces of the landfill. The article analyses the effect of the impact mitigation measures typically adopted to control PM emissions with reference to a major red mud basin located in the southwest of Sardinia (Italy). The PM dispersion models performed with the CALPUFF code (US EPA) allowed, for the case study under consideration, the estimate of the improvement provided by moistening the dry surfaces and reducing the total length travelled par year by the machinery involved in material handling, transportation and disposal
Visual impact evaluation of mines and quarries: the updated Lvi method
Full text linkThe article deals with the evaluation of the visual impact arising from quarrying, mining and civil engineering works that involve extensive surface excavation. An indirect method has been formerly proposed to quantify the Level of visual impact (Lvi) based on the two physical variables that define the magnitude of change in a natural landscape: the solid angle subtended by the visible alteration from a given viewpoint (Ωv) and the chromatic contrast between the alteration and the surrounding landscape (ΔEμ). These two objective variables are determined by elaborating the digital images of the landscape under investigation, taken from the most representative viewpoints. The Lvi indicator has proven to be highly correlated with the judgement values expressed by potential observers and thus may represent a valuable operative tool in the Environmental Impact Assessment (EIA) procedures, both for the proponent of new projects and for the governmental authorities in charge of decision-making. This article describes a further development of the Lvi method, which aims at improving the repeatability of the impact evaluation by eliminating some critical issues related to the definition of both the excavation limits and the natural comparison surfaces representing the natural landscape. To that end, the original calculation code has been implemented with two image segmentation algorithms, which objectively designate the areas within the picture to be used for the automatic calculation of the impact level Lvi. The updated code has been validated against the original Lvi method, thus confirming the suitability of the revised methodology to represent the perception of potential observers
Characterization of erodible surfaces with an environmental wind tunnel
Full text linkThe article illustrates the design and the main characteristics of the Environmental Wind Tunnel (EWT) recently built in the laboratories of Cagliari University (DICAAR). The aim of the EWT is the simulation of a part-depth Atmospheric Boundary Layer (ABL) and thus the reproduction of the wind flow over any type of surface. Experimental tests are currently being performed to analyse the correlation between the emission of dust from a variety of erodible samples and the influencing physical parameters (moisture content, percentage of silt, particles density and wind speed). The final aim of the ongoing research is the definition of reliable Emission Factors (EFs) to represent the contribution of tailing basins, mine dumps and stockpiles to the overall emission of particulate matter (PM) from industrial sites and open yards exposed to wind erosion (industrial wind erosion)
Emission of fine dust from open storage of industrial materials exposed to wind erosion
Full text linkA physical-mathematical model has been designed to estimate the emission of dust from the surface of granular materials exposed to wind erosion. The emission model implements the Monte Carlo probabilistic approach, which for a given wind velocity (i.e., shear stress velocity) ascribes the probability of saltation to the particle aggregates composing the erodible surface and calculates the emission of dust aerosol based on the main laws governing the physics of wind-blown particles. The article discusses the application of the emission code to the surfaces of two metal sulphides (PbS and ZnS), which are typically stored in stockpiles in the open yards of industrial plants that operate in the commodity sector, to be used as raw materials for the production of lead and zinc (non-ferrous metals). The results of the simulation were found to be in agreement with the indication provided by the technical literature about the emission potential of the two metal sulphides. The emission model hereby proposed intends to provide an analytical integration to the experimental and empirical Emission Factors (EF) already suggested by the technical and scientific literature about industrial wind erosion
The design of hydraulic barriers: integration between rational and observational methods
No full textHydraulic barriers can be used to control and prevent the migration of pollutants from contaminated sites to the surrounding area. Their barrier design requires a deep knowledge of the geological, geotechnical and hydrogeological characteristics of the site. Data collection and hydrogeological modeling can be very expensive, especially in complex geological conditions. Furthermore, despite the significant amount of data to be collected and the economic resources engaged, the resulting conceptual model of the site might not result sufficiently detailed as to allow a reliable design of the barrier. An alternative approach is represented by the implementation of subsequent observational phases alternated to the actual design and construction phases, so that the barrier design results the optimum for the specific site under consideration. This integrated design methodology (rational and observational) is discussed in the article with reference to a major case study located in Sardinia (Italy)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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