The abandoned lead-arsenic sulphide mine with its buildings, tailings and waste dumps along the Baccu Locci river (Villaputzu, SE Sardinia) has been rehabilitated on behalf of the communities of Villaputzu-San Vito by Integra Srl (Veneto) under supervision of Montana SpA (Milano). A total of approximately 60.000 tons of solid waste was collected from a large number of smaller waste rock dumps at the exit of mining galleries, of tailings at the ore processing plant and of sediments deposited along the braided Baccu Locci River. The solids were re-deposited in a central disposal site (CDS, see figure). First a number of terraces were excavated against a steep mountain side and then a wall was constructed at the foot of the CDS. The bottom of the CDS was covered and impermeabilized by geotextiles and a drainage system was introduced. A hydraulic-chemical treatment system, developed by GeoChemTec and tested in cooperation with the geo-environmental engineering department IGAC-CNR of the Cagliari University was implemented. A permeable reactive carbonate barrier was constructed at the foot of the CDS around a draining pipe. Subsequently, solid mining waste was mixed with appropriate amounts of iron salts to adsorb arsenate and alkaline oxides to decrease acidity of percolate and immobilize cationic metals like Al, Cd, Cu, Mn, Ni, Pb and above all Zn. At the end, the CDS was sealed by impermeable geotextiles and covered with geo-bio mats with soil to be revegetated (see spherical panorama). The Acid Rock drainage percolating from the drainage pipe is currently treated to Italian legal limits for surface water discharge by means of an unusually small external permeable reactive barrier (PRB, see spherical panorama), containing very reactive innovative porous mineral granules, specially developed by GeoChemTec. A similar PRB is currently treating Acid Mine Drainage exiting the lowest Gallery of San Riccardo, close to the ore processing plant.
As part of the EU FP7 Umbrella demonstration project executed along river Naracauli (Ingurtosu, Arbus, SW Sardinia), abandoned zinc ore waste of the Brassey processing plant was treated with transformed bauxite refinery residue and/or inoculated with bacteria, Mycorrhizae and revegetated with Euphorbia. The growth rate of the plants in function of the treatment of the ore processing waste was monitored during one year in order to establish optimum conditions for development of natural cover systems for mine tailings and waste dumps by means of soil generation and revegetation.
The mining waste water flowing from gallery Fais of the Casargiu mine into river Irvi (Montevecchio, Arbus, Sardinia) is one of the mayor Acid Mine Drainage problems of Italy. With a volumetric flow rate of more than 20 L/sec, pH ~ 6 and high concentrations of sulphate and heavy metals such as As, Cd, Cu, Mn, Ni, Pb and above all ferrous iron (200 mg/L) and Zn (1000 mg/L), treatment was not yet successful due to generation of high sludge volumes. During laboratory and field tests it was shown that the water could be well treated while mixing with relatively slow reacting alkaline mineral reagents, producing much less sludge. Subsequent filtration by well-draining, stratified solid mining waste layers, mixed with mineral reagents and organics, generated treated water obeying Italian legal limits for discharge on surface water.