Emissioni di particolato da bacini sterili esposti all'erosione eolica

The disposal of industrial and mineral processing residues (tailings) represents a major concern for human health and the diverse environmental matrices when considering the impact on soil and groundwater due to leachate filtration through the bottom of tailings basins, as well as the impact on the atmosphere caused by the wind erosion of the exposed surfaces. In fact, under unfavorable meteorological conditions (high temperature, intense solar radiation, low humidity and high wind velocity) the erosion of the dry surfaces may cause the emission of large quantities of fine and extra-fine particles (PM10 and PM2.5). Considering the significance of the issue on a global scale and the increasingly stricter orientation of international environmental policies towards a progressive reduction of harmful emissions generated by industrial activities, the need for reliable modelling tools capable of estimating the contribution of tailing basins to PM air pollution becomes apparent. The research hereby discussed specifically deals with the disposal of the red mud originated from the Bayer process (i.e. production of alumina from bauxite). Experimental emission tests were performed at the Department of Civil and Environmental Engineering and Architecture (DICAAR) of Cagliari University on red mud samples collected at a major Bauxite Residue Disposal Area (BRDA) located in south-eastern Sardinia (Italy). PM emission tests were carried out by means of the Environmental Wind Tunnel (EWT) recently designed and built at DICAAR. Before the emission tests, the red mud samples (particles assemblages and crusts) were prepared through drying processes, in order to simulate the state of the surface at the top of the BRDA (field condition), and wind speed measurements were performed into the wind tunnel to verify the accuracy of the simulated part-depth Atmospheric Boundary Layer (ABL). The emission tests were performed by adjusting the simulated wind speed to account for different intensity of the erosion phenomenon and detecting PM concentrations downstream of the samples with an aerosol monitoring system (DustTrak DRX). The Emission Factor (EF) of the red mud surfaces was calculated from the measured values of PM concentration and wind velocity, as a function of the main affecting variables (red mud water content and wind velocity).