This article deals with the problem of assisting\ud disc cutters by means of high-velocity jets of water, with\ud the aim of increasing the excavation rate while improving\ud the working conditions, with particular reference to wear.\ud The results of an experimental research undertaken at the\ud Waterjet Laboratory of the University of Cagliari on a\ud medium–hard abrasive rock clearly show that a higher\ud removal rate is achieved owing to the weakening action of\ud a jet directed on one side of the disc, causing deeper\ud penetration. This outcome is interpreted on the basis of the\ud scale formation model, which explains why smaller scales\ud are obtained on the water jet’s side of the groove.\ud Accordingly, it is suggested that the results can be further\ud improved if the jet is directed ahead of the tool along the\ud same path, since, in this way, larger scales can be produced\ud on both sides
Abstract:The implementation of European policies on environmental protection is enforcing some substantial modifications in the processing methods and technologies traditionally adopted in the alumina industry and, in particular, in the management of the alumina residue produced. The article analyses the evolution of the alumina production and the residue disposal practices in Western Europe. Some critical aspects regarding the legal implementation of the EU Directive on the landfill of waste are highlighted and discussed. With reference to the requirements established for the landfill of non-hazardous waste, a key point is represented by the possibility of reducing the deposit protection measures if the collection and treatment of leachate is not necessary. The flexibility introduced by the Directive is not incorporated into the Italian law; this fact may represent a major issue in the prospect of disposal conversion from wet to dry methods for companies operating in Italy, as it may endanger the economic sustainability of the plants' upgrade, as well as the opportunity to attract outside investments.
The 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).
The 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 (Ω v) and the chromatic contrast between the alteration and the surrounding landscape (ΔE μ). 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.
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