Structural evolution and surface reactions of microcrystalline iron oxides
Başlık:
Structural evolution and surface reactions of microcrystalline iron oxides
Yazar:
Pepper, Sarah E., author.
ISBN:
9780438043688
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (195 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Özet:
This thesis describes the evolution and transformation of iron oxides measured by synchrotron-based diffraction techniques and modern spectroscopic methods. The evolution of particles from solutions of iron (III) nitrate under basic aqueous conditions occurs in a two stage process of growth and ordering, with a first-order activation energy for the linear stage of 85.8 +/- 13.9 kJ mol-1. EPR spectroscopy suggests that the resultant particles are precursors for ferrihydrite, and have an equivalent spherical radius of 28 +/- 4 A, from SAXS spectroscopy. Synthetic 2-line ferrihydrite transforms into goethite and/or hematite, as a function of pH, under hydrothermal conditions. The activation energies, assuming first-order rate constants, for nucleation and growth are, respectively, 25.8 +/- 1.3 kJ mol-1 and 67.7 + 4.1 kJ mol-1 and for hematite 9.7 +/- 1.3 kJ mol-1 and 41.8 +/- 4.0 kJ mol-1 for goethite. The presence of aluminium or phosphate is shown to increase the induction times and lower the rate constants, thus affecting the activation energies of nucleation and growth. The presence of cadmium appears to aid the transformation from 2-line ferrihydrite, but gives hematite under conditions designed to produce goethite. In a related study, the uptake of cadmium and pertechnetate by goethite as a function of pH and ionic strength, cadmium was found to bind via a surface complexation process, whereas technetium did not bind due to the oxidised nature of the substrate. For the mineral sulfate green rust, evidence is presented which suggests that surface complexation processes dominate uptake of both cadmium and technetium. Ageing of the surface, prior to use, appears to increase the binding of cadmium. When the metal-loaded sulfate green rusts were allowed to oxidise in air, cadmium was released into solution, whereas technetium remained bound. Green rust is believed to oxidise to goethite and these results are in direct contrast to the results observed with synthesised goethite. The invariance of the binding of cadmium or technetium to sulfate green rust with ionic strength implies that the point of zero charge lies in the pH range of 6.5 to 7.5. Sulfate green rust removes technetium from solution almost quantitatively, and after oxidation, almost no technetium is released back into solution. It is proposed that this mineral has great potential for the removal and retention of technetium from solution as part of an effluent treatment process.
Notlar:
School code: 1543
Tüzel Kişi Ek Girişi:
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(684305.1) | 684305-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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