A multidisciplinary approach to assess history, environmental risks, and remediation feasability of soils contaminated by metallurgical activities.: Part B:: Direct metal speciation in the solid phase

Three soils contaminated by industrial smelting activities previously characterized using chemical and physical approaches (Part A, Venditti et al. [2000] Arch Environ Contam Toxicol [in press]) were further investigated through a complementary mineralogical approach. X-ray diffraction allowed identification of the main mineral components: carbonates (calcite, siderite) and iron oxides (magnetite, hematite, goethite) prevailed in both siderurgical soils, and siliceous compounds were more abundant in the agricultural soil. Scanning electron microscopy coupled with energy dispersive x-ray microanalysis showed that carbonates and oxides contained low amounts of heavy metals (HMs), but the potential solubility of such species under acidic conditions associated to their abundance may result in a high mobility of associated contaminants. Microanalysis also revealed peculiar minor mineral forms (metallic nodules, alloys, ore residues) that were highly informative about the history of soil contamination. Small metal-rich particles were observed (brass, lead and zinc oxides). In such compounds, HMs showed high chemical stability and were consequently poorly mobile and toxic, but also poorly removable through chemical leaching. A risk of mechanical dispersion was suggested for these particles, particularly after the chemical and/or mechanical disruption of carbonate cements. These features allowed completion and confirmation of the conclusions achieved after chemical and physical investigations, providing accurate information about the history, environmental risks and remediation feasibility of industrial soil contamination.