IMPATTI SULLA QUALITÀ DELL'ACQUA DI VECCHI IMPIANTI MINERARI: ESEMPI IN ITALIA E PORTOGALLO

Mining activity has always been one of the main engines for civilization development. Despite the well-known importance of the mining activity, it could be involved in numerous environmental issues, e.g. the presence of Acid Mine Drainage (AMD) that can originate due to the chemical reaction between atmospheric water and sulphides minerals, such pyrite and chalcopyrite. In this study four areas of mining activities were analysed. Two of them are in Italy (Servette-Eva Verda, in Aosta Valley, and Brosso, in Piedmont) and the other two in Portugal (Panasqueira and Murçós). Two sampling campaigns, on water and sediment, were conducted (during June 2022) in Italian sites. In the laboratories of the University of Turin samples. The analyses carried out on the water samples were: alkalinity test, ion exchange chromatography (for the major ions: HCO3-, Cl-, NO3-, SO42, F-, Na, K, Mg2+, Ca2+) and mass spectrometry (for the chemical elements Al, B, Ba, Cd, Co, Cu, Cr, Fe, Hg, Li, Mn, Ni, Pb, Sr and Zn). For the sediments, leaching tests were performed: samples were treated with different reagents, thus releasing different amounts of heavy metals into the aqueous solution, and as a result, the solutions were analysed. As for the two Portuguese mining sites, the chemical analyses were taken from a bibliographic research activity. Italian and Portuguese data were processed in the same procedure and approach.. The chemical analysis permitted to observe that lowest pH value (pH=2.95) can be observed in Brosso while the highest value (pH=8) can be observed in Servette-Eva Verda. Moreover, in Brosso high concentrations of iron were found (from 17.03 and 133.3 mg/L) while in Servette-Eva Verda site high concentrations for copper were observed (0.226 to 0.325 mg/L). For the two Portuguese sites, the highest concentrations were for zinc and manganese (Panasqueira zinc: 2 – 6.3 mg/L. Panasqueira manganese: 1.1 – 7 mg/L. Murçós manganese: 1.1 – 1.8 mg/L). Using the Piper trilinear diagrams, it can be deduced that all the waters were sulphate-calcium type. Concentrations of detected heavy metals and ions detected were compared with the threshold values present in the following regulations: Legislative Decree 152/2006, the European Directive of 16 December 2020 on the quality of water intended for human consumption in Portugal and the Legislative Decree 31/2001 on water potability in Italy. The same comparison was made for the sediments and the threshold in the soil and subsoil in relation to the specific intended use: sites for public, private and residential green use (Attachment 5 of Legislative Decree 152/2006). A lot of elements were above the threshold but, for example, Cr was always below the water and sediment threshold. Lastly, techniques for the environmental restoration of mines and for the treatment of Acid Mine Drainage were investigated, also hypothesizing what strategies might actually be employed in the cases of Brosso and Servette-Eva Verda.