Nature and Stability of Radiation-Induced Defects in Natural Kaolinites: New Results and a Reappraisal of Published Works

Clozel, Blandine; Allard, Thierry; Müller, Jean‐Pierre

doi:10.1346/ccmn.1994.0420601

Cited by 77 publications

(62 citation statements)

References 31 publications

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“…The principal values of g were calibrated using a 2,2-diphenyl-1-picrylhydrazyl (DPPH) standard (g DPPH = 2.0036) with an accuracy of 0.001. The spectrum of the dominant, stable, so-called A-center used for dating typically exhibits two main components named g // and g ⊥ with known values (Clozel et al, 1994).…”

Section: Epr Spectra Measurementmentioning

confidence: 99%

Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia

et al. 2018

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This study focuses on the dating of millimetric pisoliths from ferruginous duricrusts located in central Amazonia (Brazil), by coupling detailed mineralogy and two relevant dating methods: (i) (U-Th)/He analysis of goethites by mass spectrometry; (ii) analysis of radiation-induced defects of kaolinites embedded in duricrusts by electron paramagnetic resonance spectroscopy (EPR). Three samples collected at different elevations in the landscape were selected. The goethite corrected ages range from 1.1-15.2 Ma and consistently increase with elevation. EPR was performed on kaolinites after several cycles of a deferration procedure. Considering extreme geochemical scenarii, the ages of kaolinites are 1.7-7.1 Ma for a closed system and 4.0-16.7 Ma for an open system with 100% Rn loss. Ages of goethites and kaolinites are close, in the limit of the uncertainty of the methods. They show important periods of duricrust formation at Middle Miocene and at Late Miocene/Pliocene. Data allow the estimation of lowering rates between 3 and 8 m/Ma, in agreement with independent data available in the literature for the central Amazonia region or even for erosion of other cratons in the world. The two dating methods can be compared on common duricrust samples. By revealing single or multi-step weathering/erosion episodes related to relictual paleosurfaces, they also bring promising contributions to an advanced knowledge of ancient and complex lateritic geosystems.

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Section: Epr Spectra Measurementmentioning

confidence: 99%

Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia

et al. 2018

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“…The first-derivative EPR spectra is characterized by the g value, i.e., the spectroscopic splitting factor (Clozel et al, 1994). The g value is an informative parameter, because unpaired electrons in different environments have slightly different g factors, resulting in the appearance of characteristic signals for different centers at different magnetic field strengths.…”

Section: Electron Paramagnetic Resonance Spectroscopy (Epr)mentioning

confidence: 99%

“…The g value is an informative parameter, because unpaired electrons in different environments have slightly different g factors, resulting in the appearance of characteristic signals for different centers at different magnetic field strengths. The firstderivative EPR spectra of kaolinite usually consist of two regions, low-field resonances with g = 3.5-4.9, which are associated with Fe 3 § substituting for A13+, and high-field resonances with g = 2.0, which are associated with 'A' type radiation-induced defects (R/D) (Clozel et aL, 1994). In some kaolins, particularly soil kaolins with appreciable iron contents, a very broad resonance extending from g -= 3.5 to g ~ 1.5 (described also as a broad g = 2 peak) occurs.…”

Section: Electron Paramagnetic Resonance Spectroscopy (Epr)mentioning

confidence: 99%

“…All samples display signals from "A" type RID centers at g -~ 2.0, which occur in many kaolins and were assigned to a Si-O-center (Clozel et al, 1994). However, not all kaolins display RID, for example soil kaolins from relatively young red soils in Indonesia and with relatively short exposure to cosmic and mineral radiation sources do not display RID (Hart et al, unpubl.…”

Section: Electron Paramagnetic Resonance Spectroscopy (Epr)mentioning

confidence: 99%

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The Relationships between Kaolinite Crystal Properties and the Origin of Materials for a Brazilian Kaolin Deposit

Varajão

Gilkes

Hart

2001

Clays and clay miner.

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The clay particles in a kaolin deposit from Brazil were investigated by X-ray diffraction (XRD), differential thermal analysis (DTA), analytical transmission electron microscopy (ATEM), and electron paramagnetic resonance (EPR) to examine the relationships between morphological and chemical properties of the crystals and to relate these properties to formation conditions. The XRD patterns show the dominant presence of kaolinite with minor amounts of gibbsite, illite, quartz, goethite, hematite, and anatase. ATEM observations show two discontinuities in the deposit as indicated by changes in morphology and size of the kaolinite crystals. At the base of the deposit, hexagonal platy and lath-shaped particles (mean area of 001 face = 0.26 p,m 2) maintain the original fabric of the parent rock which characterizes an in situ evolution. In the middle of the deposit a bimodal population of large (mean area of 001 face > 0.05 ixm:) and small (mean area of 001 face < 0.05 p.m 2) sub-hexagonal platy kaolinite crystals occurs. This zone defines the boundary between the saprolitic kaolinite and the pedogenic kaolinite. Near the top of the profile, laths and irregular plates of kaolinite, together with sub-hexagonal particles, define two different depositional sources in the history of formation of the deposit. Crystal thickness as derived from the width of basal reflections and the Hinckley index are compatible with the morphological results, but show only one discontinuity. At the base of the deposit, kaolinite has a lowdefect density whereas in the middle and at the top of the profile, kaolinite has a high-defect density. Likewise, EPR spectroscopy shows typical spectra of low-defect kaolinite for the bottom of the deposit and typical spectra of high-defect kaolinite for the other portions of the deposit. Despite the morphological changes observed through the profile, the elemental composition of individual kaolinite crystals did not show systematic variations. These results are consistent with the deposit consisting of a transported pedogenic kaolinite over saprolite consisting of in situ kaolinized phyllite.

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“…Resonances were also observed between 200 and 400 mT, representing iron (III) ions in the external phase, as iron oxides and hydroxides dispersed by kaolin [12]. The resonance signal at 350 mT was identified and associated with radiation-induced defects (RID) [13]. This phase underwent alterations during the beneficiation.…”

Section: Resultsmentioning

confidence: 99%

Mineralogical characterization and beneficiation study of kaolin from Equador (RN) and Junco do Seridó (PB) to increase the brightness index

2017

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Kaolin is a rock composed mainly of kaolinite. It is used in many industrial segments, such as paper and ceramics. However, for these uses it is necessary to submit the ore to appropriate beneficiation, which generally involves magnetic separation and chemical bleaching, aiming to remove iron oxide and hydroxide, raising brightness index. This work reports the mineralogical characterization and analysis of the beneficiation of three samples of kaolin, two from Equador (Rio Grande do Norte -RN) and the third from Junco do Seridó (Paraíba -PB). The samples were submitted to granulometric classification in sieve of 44 mm, magnetic separation in a magnetic induction of 14000 gauss, and chemical bleaching with sodium dithionite during 240 min. The processes were divided into two beneficiation routes. X-ray diffraction, chemical analysis by X-ray fluorescence and scanning electron microscopy were used for mineralogical characterization of the ore and measurement of the brightness index, while electron paramagnetic resonance was applied to study the variation of iron oxides and hydroxides during beneficiation. The results indicate that just 30 min of chemical bleaching without magnetic separation was sufficient to increase the brightness index from 78.2 to 90.2% and from 91.3 to 95.7% in the two samples from Equador (RN) and from 86.9 to 90.4% in the sample from Junco do Seridó (PB). The magnetic separation, although causing a small increase in the brightness index, was inefficient for removal of iron oxides and hydroxides. The results indicated no need for using magnetic separation in plants for beneficiation of kaolin from these two locations, providing the reduction of production costs allowing better exploitation of the ore.

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Nature and Stability of Radiation-Induced Defects in Natural Kaolinites: New Results and a Reappraisal of Published Works

Cited by 77 publications

References 31 publications

Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia

Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia

The Relationships between Kaolinite Crystal Properties and the Origin of Materials for a Brazilian Kaolin Deposit

Mineralogical characterization and beneficiation study of kaolin from Equador (RN) and Junco do Seridó (PB) to increase the brightness index

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