Further studies of a ferrous iron doped synthetic kaolin: dosimetry of X-ray induced defects

Various physical and analytical techniques (XRD, XRF, SEM, FTIR and EPR) have been used to investigate the effects of chemical and/or physical modification of Ranong kaolin, which has been proposed as a potential bleaching clay for vegetable oils. Acid treatment after grinding resulted in major changes compared with acid treatment of the original mineral sample or mechanical treatment alone. Previous work has shown that the combined treatments produce increases in surface area and new porous structures, and the present measurements show reductions in Al:Si ratios. These are accompanied by a major reduction in O–H stretching vibrations as a result of grinding, although acid treatment produced little subsequent effect on the O–H bands in the FTIR spectra. However, acid treatment resulted in a reduction in the Al–OH–Al bending vibrations and the appearance of Si–O bands associated with newly synthesized material; these effects were much greater with samples that had been ground prior to the acid treatment. There were appreciable qualitative differences in the way in which the EPR spectra of Fe and Mn were affected; the Fe signal was sensitive to mechanical treatment, but little subsequent change was induced by acid extraction, whereas the Mn peaks were sensitive to the both the pH and the chemical nature of the acid used. These results therefore indicate that the Fe and Mn are in different types of site in the kaolin structure. Little change was observed in the main oxygen-based free radical centre associated with Si atoms, but that associated with Al was lost as a result of the treatments. Such mineral characterization is of fundamental importance to understanding the modification of kaolins and their uses as adsorbents in the food and environmental sciences.

Section: Epr Spectroscopymentioning

confidence: 60%

Characterization of modified kaolin from the Ranong deposit Thailand by XRD, XRF, SEM, FTIR and EPR techniques

Worasith¹,

Goodman²,

Neampan³

et al. 2011

“…The very sharp asymmetric two-line signal at g = 2 is attributable to stable defect centres (Angel & Hall, 1972;Meads & Malden, 1975;Herbillon et al, 1976). Similar signals were induced by X-irradiation (Angel et al, 1974X-irradiation (Angel et al, , 1977Jones et al, 1974;Cuttler, 1980Cuttler, , 1981 whereas Muller & Callas (1989) and Muller et al (1990Muller et al ( , 1992 have shown that natural kaolinites exhibit sharp g = 2 signals related to natural radioactivity. The set of resonances near g = 2 belongs to VO z+ (Pinnavaia et al, 1974;Hall et al, 1974;McBride, 1979;Monsef-Mirzai & McWhinnie, 1982).…”

Section: Resultsmentioning

confidence: 85%

Ferriferous and vanadiferous kaolinites from the hydrothermal alteration halo of the Cigar Lake uranium deposit (Canada)

Mosser¹,

Boudeulle

Weber³

et al. 1996

The uranium deposit (1350 Ma) of Cigar Lake (Canada) is surrounded by a late hydrothermal alteration halo (330 Ma) containing Fe-illites and kaolinites. Crystallochemical characterization of the kaolinites has been carried on the microscale using XRD, electron microscopy (SEM and TEM) coupled with EDX spectrometry and EPR. The large, well-crystallized particles show large amounts of Fe (0.9-1.8%) and V (0.3-0.5%). According to EPR measurements performed on both random powders and oriented samples, V occurs as the vanadyl ion VO 2 § in substitution within the octahedral sheet of the kaolinite structure in the same way as Fe 3 § Kaolinite growth proceeded through the hydrothermal alteration of anterior phyllosilicates devoid of V, induced by fluids which leached V-rich titano-magnetites in the surrounding sandstones. RESUME: Le gisement d'uranium (1350 Ma) de Cigar Lake (Canada) pr6sente une aur6ole d'alt6ration hydrothermale (330 Ma) contenant des illites ferrif~res et des kaolinites. Nous avons r6alis6 une 6tude cristallochimique des kaolinites h l'6chelle de la particule en combinant la diffraction des RX, la microscopie 61ectronique (MEB et MET) coupl6e h la spectrom6trie RX en dispersion d'6nergie et la r6sonance paramagn6tique 61ectronique (RPE). Les particules, bien form6es et de haute cristaUinit6, montrent un taux 61ev6 de Fe (0.9-1.8%) mais surtout de V (0.3-0.5%). D' apr~s les donn6es RPE, enregistr6es sur des poudres et des 6chantillons orient6s, le V apparait sous forme d'ions vanadyle VO 2+, en substitution, comme Fe 3 § dans la couche octa~drique de la kaolinite. Le ddveloppement des kaolinites r6sulte de l'alt6ration hydrothermale de phyllosilicates ant6rieurs, d6pourvus de V, par des fluides enrichis en cet 616ment lors du lessivage de titanomagn6tites dans les gr~s environnants.The Canadian uranium deposit at Cigar Lake occurs near the unconformity between the metamorphosed Lower Proterozoic basement and the Middle Proterozoic sedimentary cover. This ore deposit is surrounded by a hydrothermal alteration halo which affects the metamorphosed basement for more than 100 m depth and the Athabasca sandstones for more than 200 m above the unconformity (Fouques et al.,

“…2b) in the present work supports this interpretation, although its magnitude is much smaller that that from the B-centre (see below). Also, Cuttler (1980Cuttler ( , 1981 provided strong evidence for the association of this free radical signal with defects at the boundaries of clusters of trioctahedral cells in the normal dioctahedral structure; so it is possible that the 27 Al hfs could arise from some Alfor-Si substitution in the tetrahedral sheet.…”

Section: Free Radical Signalsmentioning

confidence: 99%

Influence of particle size on the paramagnetic components of kaolins from different origins

Worasith¹,

Goodman²

2012

AB ST R ACT : Electron paramagnetic resonance (EPR) spectra of different particle size fractions of four kaolins from diverse sources in North America, Europe and Asia have been investigated in order to characterize their paramagnetic properties and heterogeneity. There were major differences in the sources of the EPR signals from transition metals; V and Mn were structural, Fe was both structural and as associated oxides, and Cu was in the form of an adsorbed ion. The radiation-induced free radical signals commonly known as the A-and B-centres were observed in three of the deposits; however, in addition to the previously reported 27 Al hyperfine structure associated with the B-centre, we also observed much smaller 27 Al hyperfine structure on the g \ feature of the A-centre. The other kaolin sample produced four free radical signals that have not previously been reported in kaolins. Each had substantial 1 H hyperfine splitting; three are interpreted as corresponding to defect centres associated with Si-OH groups, and the other to a Si hole surrounded by protonated O atoms. The EPR spectra changed progressively with particle size, and measurements on the Asian specimens after grinding showed major differences in the Fe 3+ signals from the same particle size fractions separated from the natural samples, thus supporting previous reports that grinding results in major structural changes in the minerals.