Il progetto ha lo scopo di acquisire ulteriori dati sulla mineralogia e la geochimica delle mineralizzazioni tallifere al fine di poter meglio comprendere i meccanismi di rilascio e dispersione del tallio nell’ambiente.
Dipartimento: Dipartimento di Scienze della Terra
Data inizio: 23/09/2015
Data fine: 23/09/2018
Durata: 36 mesi
Costo progetto: 555.060 €
Finanziamento ministeriale: 555.060€
Abstract
Thallium (Z = 81) is a rare but widely spread element, having an average concentration of about 0.5 g/ton in the Earth's continental crust. It shows both a calcophile and litophile behavior and owing to its tendency to substitute alkaline metals (K+, Rb+) in rock-forming silicates (i.e. mica, feldspar), it usually does not reach concentration of economical interest. Most thallium (Tl+ and Tl3+) compounds are soluble in water and are very toxic to living organisms, more than other heavy metals. Notwithstanding its high toxicity, there is an increasing demand for thallium in the high-technology and future-technology fields, as testified by the increase of its market value, from 1278 $/kg in 1995 to 6800 $/kg in 2012. Consequently, its fascinating chemistry, its high toxicity, and its increasing economical value make thallium and its compounds of particular interest and environmental concern.
The recent finding of high thallium concentration in the pyrite ore bodies from the southern Apuan Alps, Tuscany, Italy, represents an unicum in Italy and one of the few mineralogical localities world-wide characterized by the widespread occurrence of this element. Owing to the fact that thallium has received scarce attention so far from a geo-environmental point of view since its deposits are relatively rare, southern Apuan Alps represent an invaluable area for the multidisciplinary study of thallium (mineralogy, petrology, environmental geochemistry).
The project “Thallium: Mineralogy, Geochemistry, and Environmental Hazards (THALMIGEN)” aims at studying the thallium-rich ores from southern Apuan Alps taking into account the mineralogy and geochemistry of sulfide ores and their country rocks, and the environmental hazards related to the alteration of sulfides (particularly pyrite) and the release of heavy metals, with a particular attention on the thallium pathways.
The primary sulfides and sulfosalts will be identified and fully characterized, coupling X-ray diffraction and chemical analyses, giving new data to the crystal-chemistry of these compounds, actively studied owing to their potential technological applications. A particular attention will be addressed towards the accurate crystallographical and geochemical characterization of Tl-rich pyrite. Indeed, notwithstanding the thallium production is based on the pyrite processing, the speciation of this element in pyrite is not known, i.e. whether thallium enters the crystal structure of pyrite or whether this element is hosted in nanophase inclusions in iron disulfide. This topic will be investigated through electron-transmission microscopy and spectroscopic techniques investigating the local bonding environment of thallium. The speciation of thallium in pyrite is particularly important in controlling the release of this heavy metal in the environment during the pyrite oxidation.
Oxidative processes on the primary sulfides and sulfosalts and the precipitation of Fe3+ phases from acid mine waters give rise to interesting secondary mineral assemblages, controlling the release and dispersion of heavy metals in the environment. Consequently, these phases will be fully characterized by X-ray diffraction, chemical analyses, IR and micro-Raman spectroscopies.
An accurate knowledge of thallium speciation and distribution within solid phases is a key point in the understanding of the release, transport, and distribution of this toxic element in the environment.
Finally, in order to study the potential thallium impact on the environment during both natural processes and man-made disturbance, a pilot area facing the densely populated Versilia plain has been chosen; here, the distribution and dispersion of thallium, together with the other heavy metals, will be studied collecting extensive suites of rocks, ground and surface waters, soils, and edible crops.