Structural Fe3+ in kaolinites and dickites covering a broad range of disorder was investigated using electron paramagnetic resonance (EPR) spectroscopy at both the X and Q-band frequencies. A procedure based on a numerical diagonalization of the spin Hamiltonian was used to accurately determine the second and fourth-order fine-structure parameters. A least-squares fitting method was also developed to model the EPR spectra of Fe3+ ions in disordered local environments, including multimodal site-to-site distributions. Satisfactory fits between calculated and observed X and Q-band spectra were obtained regardless of the stacking order of the samples.

In well-ordered kaolinite, Fe3+ ions are equally substituted in sites of axial symmetry (Fe(II)sites, namely Fe(II)a and Fe(II)b) which were determined to be the two non-equivalent Al1 and Al2 sites of the kaolinite structure. In dickite, Fe3+ ions were also found to be equally substituted for Al3+ in the two non-equivalent Al sites of the dickite structure. In poorly ordered kaolinites, the distribution of the fine-structure parameters indicates that Fe3+ ions are distributed between Fe(II) sites and other sites with the symmetry of the dickite sites.

Hence, when stacking disorder prevails over local perturbations of the structure, the near isotropic resonance owing to Fe3+ ions in rhombically distorted sites (Fe(I) sites) is a diagnostic feature for the occurrence of C-layers in the kaolinite structure, where C refers to a specific distribution of vacant octahedral sites in successive layers.

The substitution of Fe3+ in the kaolinite structure is studied by EPR spectrometry and by FTIR spectrometry on a large set of kaolins from different origins (sedimentary and primary ores, soil kaolins). The IR bands at 3598 and 875 cm−1, observed in the literature only in the case of disordered kaolins or in Fe-rich environments (synthetic, lateritic), are revealed by high-resolution IR analysis, whatever the origin and the total Fe content of the samples. The EPR bands corresponding to Fe3+ substituted in sites II of the octahedral sheet increase when the IR absorbance near 3600 cm−1 increases. Two IR absorption bands near 4465 cm−1 and 7025 cm−1 are observed for the first time, both in transmission and diffuse reflectance on all samples. These bands are assigned to the combination of the 3598 and 875 cm−1 bands and to the first harmonic of the band at 3598 cm−1, respectively. The area of the band at 4465 cm−1 in diffuse reflectance is quantitatively correlated to the abundance of Fe3+ located in centers II as measured by ESR. This directly confirms the assignment of the two IR bands at 3598 and 875 cm−1 to OH stretching and deformation vibration bands in octahedral FE3+ environment in the kaolinite structure, respectively. Effects due to the size of particles and to the main kaolins impurities on the near infrared spectra, are also discussed.

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 μm2) 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 μm2) and small (mean area of 001 face < 0.05 μm2) 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 low- defect 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.

IronIII for TiIV substitution in the structure of pedogenic and synthetic anatase of up to Fe/ (Ti+Fe) 0.1 mol/mol was indicated by an increase in unit cell size as measured by XRD line shifts. Mössbauer- and electron paramagnetic resonance spectra at both, 298 K and 4.2 K supported this by the presence of signals typical for octahedrally coordinated FeIII in a diamagnetic matrix. Charge compensation was achieved by structural OH, as indicated by FTIR bands at 3360 and 960 cm−1, which were absent in pure anatase and which disappeared on heating. The weight loss on heating amounted to ca. 0.5 mol H2O/mol Fe. At 600°C structural Fe was ejected, the unit cell size decreased to that of pure anatase, and pseudobrookite, Fe2TiO5, was formed.

A method is proposed to measure the absolute concentration of paramagnetic Fe3+ ions in kaolinite from various geochemical environments using powder X-band electron paramagnetic resonance (EPR) data. An Fe3+-doped corundum sample is used as a concentration standard. The Fe3+ signal is calibrated by calculating the powder EPR spectra of Fe3+ ions in corundum and low-defect kaolinite. The paramagnetic Fe3+ concentration in other samples is obtained by an extrapolation procedure. This study provides a direct assessment of the iron distribution between isolated structural Fe3+ ions and other iron species, such as Fe3+ concentrated phases and Fe2+ ions. The concentration of isolated structural Fe3+ ranges between 200–3000 ppm and represents less than half of the total iron within kaolinite crystals.

A new appraisal of radiation-induced defects (RID) in natural kaolinite, i.e., positive trapped holes on oxygen atoms, has been undertaken using Q-band EPR spectra, recorded at 93 K, of irradiated annealed and oriented kaolinite samples originating from various environments. Three different centers were identified. Two of the centers, A- and A’-centers, are trapped holes on oxygen from Si-O bonds. They have a distinct signature and orthogonal orientation, i.e., perpendicular and parallel to the (ab) plane, respectively. The third center, the B-center, is a hole trapped on the oxygen bonding Al in adjacent octahedral positions (AlVI-O−-AlVI bridge). This confirmed some previous assignments from the literature, some others are no longer considered as valid.

A least squares fitting procedure is proposed to assess the RID concentration in any kaolinite. It allows a quantitative approach of the thermal stability of RID. Isochronal annealing shows that the thermal stability of the centers decreases in the order A, A′, B over the temperature range 0–450°C: (1) B-center is completely annealed above 300°C; (2) A′-center can be annealed by heating at 400°C for more than two hours; (3) A-center is stable up to 450°C. The activation energy and the magnitude of the mean half-life for A-center is evaluated through isothermal annealing at 350, 375 and 400°C, with Ea = 2.0 eV ± 0.2, and t½ > 1012 years at 300 K. The stability of A-center seems to decrease with increasing crystalline disorder. Nevertheless, it is high enough for radiation dosimetry using kaolinites from any environment on the Earth's surface.

Two clay minerals, a dioctahedral, Na-montmorillonite from Wyoming and a trioctahedral, synthetic Na-laponite, were exchanged by cupric (Cu(II)) ions and subsequently heated at 100 °C intervals up to 500 °C. The resulting materials were analyzed by chemical analysis, X-ray diffraction (XRD), cation exchange capacity (CEC) measurements, combined thermogravimetric and differential thermal analysis (TGA-DTA), infrared (IR) spectroscopy, electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS). Montmorillonite exhibits a well-known Hoffmann-Klemen effect in that, when heated, cupric (Cu) ions migrate into the lacunae of the octahedral sheet, where they compensate the negative charge deficit of the clay layer. In the case of laponite, CEC measurements and spectroscopic measurements reveal that Cu ions migrate into the octahedral sheet where they replace Li and Mg ions. After heating at 200 °C, approximately half the interlayer Cu ions are exchanged. The exchange appears to be 1 Cu for 1 Li, resulting in a slight decrease of the negative charge of the layer. After heating at 300 °C, the remaining Cu ions are exchanged by either 1 Mg or 2 Li, which does not result in any further charge reduction. At 400 °C, some of the extracted Mg remigrates into the structure and exchanges some Li (1 Mg for 2 Li). The final product at 400 or 500 °C is then a Li-laponite with Cu(II) in the octahedral sheet.

Due to the importance of clay minerals in metal sorption, many studies have attempted to derive mechanistic models that describe adsorption processes. These models often include several different types of adsorption sites, including permanent charge sites and silanol and aluminol functional groups on the edges of clay minerals. To provide a basis for development of adsorption models it is critical that molecular-level studies be done to characterize sorption processes. In this study we conducted X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) spectroscopic experiments on copper (II) sorbed on smectite clays using suspension pH and ionic strength as variables. At low ionic strength, results suggest that Cu is sorbing in the interlayers and maintains its hydration sphere. At high ionic strength, Cu atoms are excluded from the interlayer and sorb primarily on the silanol and aluminol functional groups of the montmorillonite or beidellite structures. Interpretation of the XAFS and EPR spectroscopy results provides evidence that multinuclear complexes are forming. Fitting of extended X-ray absorption fine structure spectra revealed that the Cu-Cu atoms in the multinuclear complexes are 2.65 Å apart, and have coordination numbers near one. This structural information suggests that small Cu dimers are sorbing on the surface. These complexes are consistent with observed sorption on mica and amorphous silicon dioxide, yet are inconsistent with previous spectroscopic results for Cu sorption on montmorillonite. The results reported in this paper provide mechanistic data that will be valuable for modeling surface interactions of Cu with clay minerals, and predicting the geochemical cycling of Cu in the environment.

The influence of Cu(II) on the hydrothermal and thermal transformations of a synthetic hectorite was investigated by a combined approach using mainly X-ray diffraction, thermal analyses, and electron paramagnetic resonance spectroscopy. The presence of Cu(II) during hydrothermal treatment increased the crystallite size. Copper (II) was both structure-bound and associated with the inner surfaces of the particles. Upon heating, structural destabilization of the hectorite began at ∼400°C as indicated by the formation of free radicals. Between 600 and 700°C, the hectorite converted to enstatite, and in the presence of Cu(II), to enstatite and richterite. The formation of richterite as an additional conversion product is explained by the creation of structural weakness due to structure-bound Cu(II) in F-containing hectorite. Our results suggest that traces of Cu(II), typical of natural environments, may influence the conversion products in high-temperature geochemical systems.

The adsorption mechanisms of divalent cations in zeolite nanopore channels can vary as a function of their pore dimensions. The nanopore inner-sphere enhancement (NISE) theory predicts that ions may dehydrate inside small nanopore channels in order to adsorb more closely to the mineral surface if the nanopore channel is sufficiently small. The results of an electron paramagnetic resonance (EPR) spectroscopy study of Mn and Cu adsorption on the zeolite minerals zeolite Y (large nanopores), ZSM-5 (intermediate nanopores), and mordenite (small nanopores) are presented. The Cu and Mn cations both adsorbed via an outer-sphere mechanism on zeolite Y based on the similarity between the adsorbed spectra and the aqueous spectra. Conversely, Mn and Cu adsorbed via an inner-sphere mechanism on mordenite based on spectrum asymmetry and peak broadening of the adsorbed spectra. However, Mn adsorbed via an outer-sphere mechanism on ZSM-5, whereas Cu adsorbed on ZSM-5 shows a high degree of surface interaction that indicates that it is adsorbed closer to the mineral surface. Evidence of dehydration and immobility was more readily evident in the spectrum of mordenite than in that of ZSM-5, indicating that Cu was not as close to the surface on ZSM-5 as it was when adsorbed on mordenite. Divalent Mn cations are strongly hydrated and are held strongly only in zeolites with small nanopore channels. Divalent Cu cations are also strongly hydrated, but can dehydrate more easily, presumably due to the Jahn-Teller effect, and are held strongly in zeolites with medium-sized nanopore channels or smaller.

The tropical weathering of sedimentary kaolin deposits from the plateaux surrounding Manaus (Alter do Chao formation, Amazon basin, Brazil) leads to the in situ formation of thick kaolinitic soils. The structural changes of kaolinite have been investigated quantitatively by infrared spectroscopy and electron paramagnetic resonance. Both techniques consistently show that each sample contains two types of kaolinite in various proportions. The progressive decrease in kaolinite order from the bottom to the top of the profile results from the gradual replacement of an old population of well-ordered kaolinite, typical of the underlying sedimentary kaolin, by a more recent generation of poorly ordered soil kaolinite. The vertical pattern of kaolinite replacement differs from that of the transformation of Fe oxides and oxyhydroxides previously observed in the same profile. The inherited fraction of well-ordered kaolinite ranges from 60% at a depth of 9 m to 30% in the upper levels of the soil. The persistence of sedimentary kaolinite in the upper horizons suggests that the rate of kaolinite transformation is relatively slow at the time scale of lateritic soil formation. Kaolinite inheritance unlocks the lateritic record of past weathering conditions.

Electron paramagnetic resonance (EPR) spectroscopy is a well-established method of dating based on trapped charges, applied to various crystalline materials, including carbonates, bones, and teeth. It provides a detailed insight into the structure of radiation defects—paramagnetic centers generated by irradiation, without the need of a painstaking sample preparation, often challenging in other methods. Using EPR we studied the effect of γ radiation on lime mortars and plasters from ancient settlement Hippos in Israel, in order to analyze the process of defect generation. Analysis of the complex spectra revealed the presence of radiation-induced species, including CO2–, NO32– and organic radical. Using an artificial UV source, we generated relatively strong signals of paramagnetic centers, analogous to those created by γ irradiation, reaching their maximum intensity after 5–6 hr of UV exposure. Our results confirm the previous reports that radiation defects can also be generated, instead of bleached, in calcite by UV radiation, which is crucial for identifying the issues related to light exposition, affecting the accuracy of age determinations in trapped-charge dating methods.

In this issue, MacDonald et al have used data from the South London and Maudsley NHS Foundation Trust electronic patient record to investigate the relationship between service change, routine outcome data and ‘continuity of care’. The period they have looked at was one of huge change in the configuration of services and the background to this is explored here.

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 27Al hyperfine structure associated with the B-centre, we also observed much smaller 27Al 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 1H 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 Fe3+ 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.

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.

The results of EPR, UV-VIS and IR spectral studies show that benzimidazole forms various complexes with Cu(II) exchanged in the interlayer space of montmorillonite, depending on the acidity of the reaction medium during synthesis. In a nearly neutral solution a bis(benzimidazole)bis(aqua) Cu(II) cationic complex is formed. In a strongly basic solution, benzimidazole is bound to Cu(II) in the form of an anionic bifunctional ligand and a planar intercalated bis(benzimidazolate) Cu(II) complex is formed, where the benzimidazolate anion acts as a bridging ligand in the polymeric complex. The treatment in basic solution leads to partial illitization of the smectite. In a strongly acid solution, a nearly stoichiometric ionic exchange of benzimidazolium ion for Cu(II) ions takes place in the interlayer space of montmorillonite.

Three raw samples of Fe-rich smectites from Gafsa (Jebels Shemsi and Hammadi, Tunisia) have been characterized by different techniques which indicate that they contain (15 – 20%) illite, probably interstratified and to a lesser extent they also contain kaolinite, calcite, quartz and Fe oxides. These samples present a relatively high Fe content (∼9%) in the <2 μm fraction. From EPR and Mössbauer spectroscopy it is deduced that Fe is mainly present as Fe(III) in the octahedral environment of smectites and also in Fe-oxyhydroxides associated with the clays. Aluminium-pillared clays have been prepared from the Na+-purified samples, and their thermal stability and acidity have been studied.