Effect of Adsorbed Iron on Thermoluminescence and Electron Spin Resonance Spectra of Ca-Fe-Exchanged Montmorillonite

Abstract

Abstract-The electron spin resonance (ESR) spectra and the natural and gamma-induced thermoluminescence (TL) glow curves of a series of variably cation-exchanged Fe-Ca-clays prepared from SWy-1 montmoriUonite were examined. The ESR signal (g = 2) intensity associated with the surface Fe was found to increase linearly with surface Fe content up to a nominal concentration of 50% exchangeable Fe. At > 50% exchangeable Fe, no appreciable increase in the signal was noted. The TL intensity decreased linearly with increasing surface Fe up to 50% nominal exchangeable Fe. At > 50%, the signal was not appreciably further diminished. The natural TL showed only a high-temperature peak, but irradiation produced an additional low-temperature peak. One month after gamma-irradiation, the integrated TL signal was still 10-100 times higher than that from the non-irradiated material. Thus, (1) surface iron clusters may form above a certain critical Fe concentration; (2) the Fe clusters are probably less effective in quenching TL than are single Fe atoms, implying interaction between surface Fe and the stored energy content of the material; and (3) the electronic energy stored in the material as the result of gamma-irradiation is only slowly dissipated.

Cation Migration in Smectite Minerals: Electron Spin Resonance of Exchanged Fe3+ Probes

“…As the Fe 3+ content of both the montmoritlonite and the Laponite increased, the intensity of the broad g = 2.0 signal increased. The spectra of the montmorillonite samples are qualitatively similar tO those obtained by Coyne and Banin (1986), who used a natural montmorillonite and the ion-exchange method of Banin (1973). Our spectra are also similar to those obtained by Evmiridis (1986) for Fe3+-exchanged zeolites and show promi- nent signals at g = 4.3.…”

“…Most researchers agree that these signals of this type arise from exchange interactions between clusters of Fe 3 § ions that may be present on the surfaces of the smectite as iron oxide-oxyhydroxide impurity phases (Goodman, 1978) or within interlayers (Gracium and Meghea, 1985;Che et al, 1974). For Fe3 § montmorillonite, Coyne and Banin (1986) attributed a similar signal, which increased with percentage of Fe 3+ exchange, to hydrated surface iron. Species of the type [Fe(OH)(H20)5] 2 § are probably sufficiently distorted to give a very broad signal at g = 2 and are probably present within the interlayers of hydrated Fea § smectites in which increased polarization of water molecules in the restricted environment causes the water molecules to dissociate (Mortland and Raman, 1968).…”

Residual Manganese(II) Entrapped in Single-Layer-Hydrate Montmorillonite Interlayers

“…Natural montmorillonite, however, yields well-resolved EPR spectra without interlayer collapse (Coyne and Banin, 1986). Recently, Gehring and co-workers Gehring et al, 1993) have developed a methodology to determine the coordination environment of paramagnetic cations [e.g., Fe(III), V(IV)] in clay minerals without chemical pretreatment.…”

“…Manganese (II) could yield HFS signals either as an isomorphically substituted species or as an adsorbed species on the clay mineral surface. The easy exchangeability of Mn(II) in SWy-1 montmorillonite (Coyne and Banin, 1986) is inconsistent with the presence of Mn(II) in a structural site. Therefore, the EPR spectra can be attributed to Mn(II) located in interlayers.…”

Method development for evaluating the redox state of Callovo-Oxfordian clayrock and synthetic montmorillonite for nuclear waste management

“…In our study we will focus on the behavior of iron in montmorillonites, which are a very common smectite present in natural clays, claystone and soils (Bergaya et al, 2006). Iron on montmorillonite could further be present as the clay exchange complex Choudary et al, 1994;Coyne and Banin, 1986;Diamant et al, 1982;Ebitani et al, 2002;Helsen and Goodman, 1983;Hirt et al, 1993;Johnston and Cardile, 1987;Kamei et al, 1999;Letaief et al, 2002;Thompson and Tahir, 1991). Structural iron could be occurred in either the octahedral or tetrahedral sheets by replacement of Al 3+ (Reinholdt et al, 2001) or Si 4+ , or in pillars bridging two individual clay particles as in the ''pillared clays'' (Bergaya and Barrault, 1990;Bergaya et al, 1991;Chirchi and Ghorbel, 2002;Komadel et al, 1994;Mishra and Parida, 1998;Mody et al, 1993;Pálinkó et al, 1996;Rightor et al, 1991;Wasserman et al, 1998).…”