Detall

Conferència: Mineralogical engineering and environmental protection

Notícia | 08-11-2006

Dr. Marcello Mellini, Dip. Scienze della Terra-Universià di Siena
Sala d'Actes de l'Institut de Ciencies de la Terra "Jaume Almera", a les 12h del migdia

The circulation of inorganic contaminants (acid mine drainage, heavy metals, radioactive elements, and so on) follows pathways closely ruled by crystalchemistry, mineralogy and geochemistry. These disciplines may be usefully exploited to hopefully minimize any risk, designing possibly not hazardous scenarios, as in the next examples.
Sulphuric acid waste: production plants (e.g., titanium dioxide) may result into huge amounts of sulphuric acid waste. This may be neutralized by reaction with calcium carbonate, producing gypsum and carbon dioxide. The neutralization cycle may become environmentally and economically substainable by an as-more-as-possible close production cicle, namely provided that a) the dumped waste is minimized; b) the waste by-products are separated and re-used; c) the value of each chemical by-product is maximized by confering some special property; d) rather than a fresh material, the neutralization reactants are wastes from some other activity.
Also mine dumps (mostly, from pyrite-rich ores) may release strongly acidic waters, capable to dissolve several elements. In some cases, these anthropically modified sites show spontaneous mechanisms capable to reduce metal loads and/or water acidity; these processes may suggest more efficiently designed risk-reduction treatment processes, possibly leading even to metal recovery .
Natural arsenic traps: arsenic represents one of the most dangerous contaminants; it is released by natural weathering, mining activity, overpumping and lowered water table. To understand how arsenic is released and mobilized, we looked for existing examples of arsenic traps. The case occurs with iron ochres present in Monte Amiata (Italy), mostly consisting of iron hydroxide (goethite) and containing up to ten percent As2O5. They constitute a valuable natural laboratory, where to test the effective long-term storage of arsenic adsorbed on goethite.
Cesium trapping: stabilization of cesium waste requires phases capable to deal with its large ionic radius. By comparison of Cs-tetra-ferri-annite, Cs-annite, CsAlSiO4, Cs-montmorillonites and Cs-zeolites, Cs-tetra-ferri-annite seems the best candidate for long-term storage of cesium radioisotopes. It is the mica with the largest unit cell volume; it is synthesized under easily attainable hydrothermal conditions; its structure does not change over a gradient of 23°C/km. Leaching tests show that it is the most leaching-resistant phase (followed by CsAlSiO4, Cs-montmorillonites and Cs-zeolites) at different temperatures, pH and reaction conditions.

Depleted uranium: depleted uranium has been widely used to build quite a range of military weapons, abundantly used in the Kosovo and Irak wars as bullets capable to penetrate through tank shields and thick concrete walls, in the same way as a hot knife cuts butter. Dangerous to soldiers and civilians when shot, even after the battle the uranium oxide particulate and the uranium bullets may constitute a long-term reason of concern, as due to uranium leaching, as shown by the case of a depleted uranium penetrator we collected in Djakovica, Kosovo.


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