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Sphalerite tailings are the most important type of waste in the mining district of Sardinia. This situation justifies the interest in the applicability of flotation as a remediation technique by which declassify the tailings (reducing the concentration of heavy metals). The flotation of mine tailings represents a novelty if aimed at environmental remediation. Instead, it is a widespread industrial practice for recovering secondary raw materials. In this case, the scientific aspects are rarely explored: this situation explains the limited number of cases examined, the review of which, however, represents a necessary premise for the research undertaken. Furthermore, the availability of industrial case demonstrates reprocessing is not only a technically possible process but also of economic interest. After an overview of the environmental problem in abandoned mining areas, the paper recalls the fundamental elements useful for developing a comparison between the main operating methods adopted in the flotation of Pb and Zn sulphides, both as primary ores (high and low Zn content) and as tailings. The case history also includes the treatment of Zn oxidized compounds. The comparison demonstrates that the treatment of sphalerite tailings can follow the same approach as that of low-grade primary ores, but with evident economic advantages, and allows achieving those, far greater, of the multiple environmental effects.

The main aim of this research is to find a feasible way to reuse mud cuttings from ornamental stone, such as trachyte and basalt, normally disposed of in landfills, using it in the production of full and/or aerated bricks for civil purposes. The study examined the characteristics of full bricks produced with mud cuttings from ornamental stone including, resistance to uniaxial compression, water absorption and apparent density of mud alone or when mixed with two types of clay at different firing temperatures. As temperature rose, the strength and density of the samples increased, while absorption decreased. The use of clay improved the sintering process during firing, giving a less porous and mechanically stronger material that normally used to produce full bricks for civil constructions. For the second type of product, aerated bricks, the study investigated porosity, density, resistance to uniaxial compression and the thermal insulation capacity of bricks made by adding lime and aluminium powder to trachy...

Laboratory tests were carried out to determine the primary parameters affecting the efficiency of the process of leaching heavy metals from natural soil collected inside a metallurgical plant in Italy. The soil samples tested consisted primarily of medium density, fine silica sand that had been contaminated with lead and zinc metallurgical wastes by percolating rainwater. Samples were obtained 1–2 m below ground level in an area where the surface consists of artificial strata composed of soil mixed with metallurgical solid waste. The soil layer tested hosts a low-permeability aquifer (at depths generally greater than 10 m below ground level) that is also contaminated by heavy metals. Batch leaching experiments were conducted using acid solutions (acetic, nitric, hydrochloric and sulphuric) as extracting agents. During leaching tests, concentrations of Zn, Pb, Cd, Cu, Mn and Al were monitored. The results indicate that the best leaching solution varies for all analytes and soil samples examined. Statistica...

In the last two centuries, several Pb–Zn mines were active in the Rio Mannu basin near Narcao (SW Sardinia, Italy), but are now abandoned. These abandoned mines pose a serious risk to the population and required an assessment of the hazard sources and the contaminant pathways in the area. The characterization plan of the Rio Mannu basin was carried out according to Italian protocols. Specifically, samples of soil, stream sediment, fine-grained ore-processing waste (from washery and flotation processes), surface water and groundwater have been analyzed in order to assess the levels of contamination in each mine area and the risks in the plains surrounding the site. Several potential chemical contaminants were considered both in solid materials and water samples. The Rosas mine was recognized as the most contaminated area in the basin, due to the presence of a large tailing pond, some fine-grained waste piles and two mine adits with concentrations of the toxic elements As, Cd, Cu, Pb, Sb and Zn exceeding Italian regulatory standards. The dispersion of contaminants occurs downstream from the small stream draining the area. In case of heavy rain the runoff into the streamlet transports the contaminated material far into the plain. The results of this study show that the characterization plan is a relatively cheap tool for establishing mitigation actions, prior to the realization of a complete, and usually expensive, remediation project at abandoned mine sites. Urgent recommended actions in the Rio Mannu basin include the treatment of the adit water prior to its discharge into the Rio Barisonis; the construction of drainage barriers on waste piles to reduce runoff and solid transport into the Rio Barisonis; the consolidation of the earthen dam containing the tailing pond of Rosas to avoid the deepening of erosion furrows that may threaten its stability.