1,721,001 research outputs found
Ferro nanoscopico per la bonifica di acquiferi contaminati
No full textNell'ambito della bonifica di matrici ambientali inquinate, ed in particolare dei sistemi acquiferi, l'utilizzo di ferro zerovalente di dimensione nanometrica risulta essere una delle tecniche più interessanti e promettenti. Il ferro nanoscopico (nanoscale zerovalent iron - NZVI), caratterizzato da particelle di diametro estremamente piccolo e compreso tra 1 e 100 nm, da elevatissime superfici specifiche e da reattività superiori rispetto a quelle del ferro millimetrico, può essere iniettato direttamente in falda, sotto forma di dispersione colloidale, per trattare un'ampia gamma di contaminanti organici ed inorganici e per consentire il superamento dei limiti geometrici imposti dalla realizzazione di barriere reattive permeabili.
Partendo da una trattazione di tipo generale lo studio affronterà i temi della produzione, della caratterizzazione, della mobilità e del trasporto del ferro nanoscopico in mezzi porosi saturi, prendendo in considerazione sia i vantaggi legati all'uso di questi materiali, sia gli aspetti ancora controversi e da indagare ulteriormente
Biogeochemical characterization of zerovalent iron reactive barriers
No full textIn this study, we have investigated the geochemical processes taking place within a Fe0 barrier at the field installation of Avigliana, near the city of Turin in Italy, which represents the first full-scale application of this technology in Italy (Di Molfetta & Sethi, 2005
Characterization of nanoscale iron for groundwater remediation
No full textThe aim of this study is the characterization of nanoscale zero-valent iron (NZVI), used for the remediation of contaminated groundwater. This is one of the most prominent applications of nanotechnology in environmental field. Compared to the commonly used granular zero-valent iron, nanoscale zerovalent iron (NZVI) particles show a larger surface areas that leads to higher reactivity towards a wider variety of environmental contaminants. Moreover, due to the small diameters of the particles (1-100 nm) they can be injected in the subsurface as a colloidal suspension, thus providing great flexibility for in situ applications. We performed laboratory analysis on RNIP-10AP-SDS, a nanoscale iron slurry produced by Toda Kogyo Corp. We investigated chemical and physical properties either on dispersion or on its single phases (dispersed phase constituted by nanoscale iron particles and dispersing medium constituted by water solution with a biodegradable polymer). The dispersion was analyzed to determine the composition by I.C.P.-M.S. and the morphology by optical microscope and E.S.E.M. In order to investigate the surface, the morphology and the crystallography of nanoscale particles, we performed studies by X-ray diffractometry (X.R.D.), IR spectroscopy, scanning and transmission electron microscopy (SEM, TEM), BET measurements. All these analysis were performed on dried iron nanoparticles. The characterization on dispersed phase showed that particles of NZVI tend to aggregate, producing clusters that may approach microns in size. Characterization analysis were performed also on polymer by IR.-A.T.R. spectroscopy. These results suggest that the RNIP dispersion is unstable. Consequently, some uncertainties still limit the application of NZVI: (1) the reactivity and longevity over extended period of time; (2) the aggregation potential and transportability in saturated porous media; (3) potential release of pollutants (e.g. heavy metals
Anti-oxidant/pro-oxidant activity of ascorbic acid: Effect in the degradation of Acid Orange 7 with H2O2 catalyzed by transition metal ions
No full textHydrogeochemical and biological processes affecting the long-term performance of an iron based permeable reactive barrier
No full textDespite the wide diffusion of zero-valent iron (Fe0) permeable reactive barriers (PRBs), there is still a great uncertainty about their longevity and long-term performance. The aim of this study is to investigate the biological and the hydrogeochemical processes that take place at a Fe 0 installation located in Avigliana, Italy, and to derive some general considerations about long-term performance of PRBs. The examined PRB was installed in November 2004 to remediate a chlorinated solvents plume (mainly trichloroethene and 1,2-dichloroethene). The investigation was performed during the third year of operation and included: (1) groundwater sampling and analysis for chlorinated solvents, dissolved CH4, dissolved H2 and major inorganic constituents; (2) Fe0 core sampling and analysis by SEM-EDS, XRD, and FTIR spectroscopy for the organic fraction; (3) in situ permeability tests and flow field monitoring by water level measurements. The study revealed that iron passivation is negligible, as the PRB is still able to effectively treat the contaminants and to reduce their concentrations below target values. Precipitation of several inorganic compounds inside the PRB was evidenced by SEM-EDS and XRD analysis conducted on iron samples. Groundwater sampling evidenced heavy sulfate depletion and the highest reported CH 4 concentration (>5000 μg/L) at zero-valent iron PRB sites. These are due to the intense microbial activity of sulfate-reducers and methanogens, whose proliferation was most likely stimulated by the use of a biopolymer (i.e. guar gum) as shoring fluid during the excavation of the barrier. Slug tests within the barrier evidenced an apparent hydraulic conductivity two orders of magnitude lower than the predicted value. This occurrence can be ascribed to biofouling and/or accumulation of CH 4(g) inside the iron filings.This experience suggests that when biopolymer shoring is planned to be used, long-term column tests should be performed beforehand with initial bacterial inoculation and organic substrate dosing, in order to predict the eff ects of bacterial overgrowth and gas generation. During construction particular care should be taken in order to minimize the amount of used biopolymer so that complete breakdown can be achieve
Fe- and V-doped mesoporous titania prepared by direct synthesis: Characterization and role in the oxidation of AO7 by H2O2 in the dark
No full textTwo metal-doped mesoporous titania samples (Fe-MT and V-MT) have been prepared, and characterized through several techniques (N2 sorption at - 196°C, XRD, TEM, XPS, DR-UV-Vis and Raman spectroscopies). As reference, pure mesoporous titania (MT) and commercial non-porous P25 (Degussa) were considered, the latter both as such and after impregnation with either Fe- or V- salts (Fe-IT, V-IT). In addition, the catalytic activity of the samples has been measured in the oxidation by H2O2 in water of Acid Orange 7 (AO7), a model azo-dye. Catalytic measurements were run at natural pH of the AO7 solution (= 6.8), to avoid adsorption phenomena occurring in acidic conditions, and, contrary to what usually done, in the absence of light. It is inferred that with Fe-MT inclusion of Fe(III) takes place, so that Fe(III) ions are present both in the bulk and at the surface, whereas with V-MT V species are present basically only at the surface. As to AO7 degradation: i) titania alone is already rather active, with MT more active that P25, likely because of the higher specific surface area (SSA); ii) impregnated samples are more active than P25, because of a positive catalytic effect of metallic centres; iii) synthesized samples are more active than corresponding impregnated ones, not only because of the higher SSA, but also because direct synthesis allows a better dispersions of active sites; iv) Fe- containing samples are more active, in the long run, than V-containing ones, because of a different reaction mechanism (Fenton-like and Mars van Krevelen, respectively). The occurrence of two mechanisms is shown by a different time course in the two cases. Further support comes from XPS data, showing that, after reaction Fe-MT still features only Fe(III) species, whereas V species in V-MT are basically reduced to V(IV), which leads to deactivation of these sample
Fe-TiO2 and V-TiO2 mesoporous catalysts obtained by direct synthesis: physico-chemical characterization and catalytic properties in the decomposition of azo-dyes
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