Application of Electron Paramagnetic Resonance and Mössbauer Spectroscopy in the Investigation of Kaolinite-Group Minerals

Abstract

Abstract--Samples of nacrite, dickite, kaolinite, and halloysite were investigated using X-band electron paramagnetic resonance (EPR) and Mbssbauer spectroscopy. Fe 3+ gave rise to EPR signals at g = 4 which differed with the individual polytype. Only nacrite had no resonance in this region of the spectrum, but it had one at g ~ 2. Dickite had a quadruple line, kaolinite a triple line, and halloysite a single line in this region. The EPR spectra of these minerals are apparently dependent also on the orientation of adjacent layers in the structures. Other resonances were attributed to (1) clusters of ferric ions giving rise to broad resonance near g = 2, (2) trapped holes, and (3) free radicals linked with organic matter. The Mbssbauer spectroscopic results suggest that iron occurs in the ferric state (except in nacrite where Fe 2+ is present also) as an ionic substitution (IS) in octahedral layers. This suggestion follows from the difference is the IS values between octahedral and tetrahedral symmetry sites occupied by Fe a+ equal to -0.4 mm/sec. Linewidths depend mainly on the way the layers stack; for monoclinic modifications represented by nacrite and dickite, the linewidths are narrow (F = 0.45 mm/sec and 0.56 mm/sec, respectively); pseudomonoclinic halloysites also gave narrow linewidths (F = 0.39 mm/sec and 0.48 mm/sec). The widest line was observed for triclinic kaolinite (F = 0.62 mm/sec and 0.71 mm/sec).

Electron spin resonance study of donor-acceptor sites in Zr-montmorillonite

“…This band has already been observed for various clays (Olivier et al, 1975;Komusinski et al, 1981;Pinnavaia, 1981) and attributed to the Fe 3+ ions substituted in octahedral sites. The position of this peak is not likely to disturb the observation of signals due to Pe and TCNE.…”

Mössbauer Effect Studies of Iron in Kaolin. I. Structural Iron

“…One question which needs consideration is why low temperature paramagnetic hyperfine splitting of kaolin structural iron has not been observed previously. The room temperature spectra of various kaolins in the literature suggest relaxed behavior in several samples (e.g., Jefferson et al, 1975;Komusinski et al, 1981), although it appears to have been overlooked. One possible reason is that the spectra in question may have been obtained with an experimental configuration that resulted in baseline curvature even for non-relaxed spectra.…”

“…Centers IIA and IIB are associated with Fe 3+ in regions of high crystallinity and regular stacking, and the difference between the two has been attributed to the existence of two distinct orientations of surface OH groups (Hall, 1980). Although these three sites are not resolved in the room temperature Mtssbauer spectrum of kaolinite, Komusinski et al (1981), in an ESRMtssbauer study of a variety of kaolins, noted a correlation between the Mtssbauer linewidth and the number of Fe 3+ sites detected by the ESR measurements. The paramagnetic HFS spectra arising from each of the three sites are expected to be somewhat The values of A, Ay, Az, the hyperfine interaction constants determining the coupling between the total electronic and nuclear angular momenta S and I, respectively, depend on the symmetry of the crystal field splitting, and Wickman et al (1966) have calculated their variation as a function of X.…”

Physical and chemical study of lattice kaolinites and their interaction with orthophosphate

“…Furthermore, the widest line (G = 0.62 and 0.71 mm s -1 ) indicate the presence of a triclinic kaolinite with layers infl uenced by diff erences in layer stacking of polytypes as well as by degree of layer stacking order. (Komusinski et al 1981).…”