Giampaolo Orrù

Recycling of sludge from ornamental stone processing as resource in civil constructions

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 trachyte mud at different sintering temperatures, ranging between 980 and 1040 °C. As temperature increased, it was observed that an increase in the resistance and density of the samples was accompanied by a reduction in the heat-insulating capacity. When compared with commercial aerated bricks, it was found that aerated bricks obtained from trachyte sludge cuttings and fired at temperatures below 1030 °C, have a greater thermal insulation capacity but a lower mechanical resistance, restricting their use to non-load-bearing masonry applications.

Heavy metal leaching of contaminated soils from a metallurgical plant

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. Statistical analysis was used to identify correlations between efficiency and leaching rate.