AMIANTO NEL POLO PETROLCHIMICO DI SIRACUSA: CARATTERISTICHE MINERALOGICHE E FISICHE DI UN MATERIALE LARGAMENTE UTILIZZATO

In the second half of the last century, asbestos had been widely used in the industrial area of Priolo and Augusta, in Syracuse province (Sicily, Italy), before being definitively banned in 1992. This research has permitted to reconstruct the use of asbestos-containing materials in the petrochemical industry and shipyards of this area, starting from an accurate historical census. Once the asbestos sheeting had been identified as a commonly used material, then the operation temperatures were reproduced under laboratory conditions in order to assess both the physical and mineralogical transformations in the asbestos. Both tensile and pull up tests were carried out which highlighted good mechanical characteristics of the samples from the asbestos sheets which had not been thermally treated. Nevertheless, these mechanical characteristics suddenly deteriorate with increasing temperature and, consequently, the tensile strength of the material is strongly reduced, so much that, at the end of this process, the pull up test shows a radical deterioration of the material. These data can be related to the fiber release potential, which linearly increases with the treatment temperature of the materials, therefore proportionally increasing both the fiber release hazard and the risk of pathogenicity. The microscopic analysis showed that the higher the treatment temperature is, the more rearranged the texture will be, according to the assessment process of the mechanical characteristics. The chemical-mineralogical investigation carried out by SEM and DRX methods detected some fibrous structures which tend to remain in those samples which are subjected to a thermal treatment. The typical elongated, sinuous and rolled morphology of the fibers, along with the objective evidences from the peaks of the DRX diffractograms, clearly highlight the presence of chrysotile. It is worth noting that the chrysotile is well recognizable in the samples which are heated up to the temperature of 550° and not in those which are heated at 750°, when talc and forsterite generate from the transformation of serpentine and the contemporaneous loss of hydroxyl groups. One of the most interesting results from the SEM analysis is that the habitus of the olivine, which originates from chrysotile and is generally expected to be prismatic, maintains its fibrous aspect instead. In the natural state, indeed, if the passage from chrysotile to olivine occurs suddenly, this transformation is topotactic, i.e. it occurs by ionic diffusion of Mg and Si, leaving the oxygen lattice unchanged as much as possible. This mechanism leads to a high level of pseudomorphosis of the olivine which tends to maintain a microscopically fibrous structure.