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.

In the electrocoagulation process a suspension of kaolinite and bentonite is coagulated by electrochemical treatment where aluminum anodes are dissolved and aluminum ions react with clay particles, forming flocs which precipitate. Several factors affecting the efficiency of electrocoagulation are investigated. They include NaCl concentration, voltage, and flow conditions within the cell. Increased NaCl concentration led to lower electric resistance and cleaner running electrodes. Enhanced shear associated with recirculation resulted in clear supernatant and more compact floes. While increasing the feed rate, which was equivalent to decreasing aluminum concentration through the system, reduced cake height but increased turbidity.

Smectite single crystals of superior quality were synthesized at high pressures and temperatures using a modified belt type high pressure apparatus. Pressure-temperature conditions were established for smectite formation by quenching experiments in the pressure range from 2–5.5 GPa and temperatures of 700°–1000°C. Smectite crystals with extraordinary quality were formed beyond 3 GPa and 1000°C with coexisting phases of coesite, kyanite, jadeite, and in some cases with mica and glass. Smectite was confirmed from the XRD taken after intercalation of ethylene glycol. The smectite crystals were considered to be quenched crystals metastably from the hydrous silicate melts formed at high pressures and temperatures.

The “modified chlorite structure” forms by the dehydroxylation of the interlayer octahedral sheet of magnesian chlorite at around 500°C and results in a structure with a basal spacing near 27 Â (Brindley and Chang 1974). This process involves drastic textural modifications as indicated by gas adsorption experiments which reveal the formation of structural micropores. Infrared spectroscopy as well as thermogravimetry and mass spectrometric analysis show that these micropores are filled with molecular atmospheric water, carbon dioxide, nitrogen, argon and hydrocarbons which condense once the samples cool down. A high temperature treatment is needed in order to release the different phases. A heterogeneous dehydroxylation mechanism is proposed in which micropores are formed in donor regions and magnesium and oxygen are concentrated in acceptor regions. This leads to a 27 Å structure with micropore zones and enriched interlayer oxide zones alternating along the z-axis of the mineral.

Clay samples of greenish colour were collected from submarine hydrothermal chimneys of the Galapagos Rift and Mariana Trough. Mineralogical and chemical investigations of the clay by scanning and transmission electron microscopy, X-ray diffraction, differential thermal analysis, infrared-spectros-copy, X-ray fluorescence, and determination of specific surface area, and oxygen isotope composition identify it as a well crystallized nontronite. This nontronite of hydrothermal origin has a nearly monomineralic character, a low Al-content, and a formation temperature of 21.5 to 67.3°C. The most remarkable characteristic, however, of the nontronite deposit is its microstructure, a network of microtubes composed of fine frequently folded clay sheets. These delicate filaments show close similarity in size and form to sheath forming bacteria. The correlation between clay mineral and chemical characteristics, as well as biological conditions at marine hydrothermal smoker chimneys, let us suggest that Fe oxidizing, sheath forming bacteria are playing a decisive role in nontronite formation at these sites.

Interlayer cations and moisture content greatly influence the molecular vibrations of H2O in montmorillonite as shown through reflectance spectroscopy in the infrared. The absorptions due to H2O have been studied in montmorillonites exchanged with H, Na, Ca, Mg and Fe3+ interlayer cations under variable moisture environments. Band assignments have been made for absorptions in the 3 µm region due to structural OH vibrations, symmetric and asymmetric H2O stretching vibrations and the H2O bending overtone. Changes in the energies of the absorptions due to H2O stretching vibrations were observed as the samples were dehydrated by reducing the atmospheric pressure. Absorptions near 3620 cm−1 and 3550 cm−1 have been assigned to water bound directly to cations (inner sphere) and surface-bonded H2O and absorptions near 3450 cm−1 and 3350 cm−1 have been assigned to additional adsorbed water molecules. Band assignments have been made for combination bands in the near-infrared as well. Absorptions near 1.41 μm and 1.91 μm are assigned to bound H2O combination bands, while the shoulders near 1.46μm and 1.97 μm are assigned to combinations of additional H2O molecules adsorbed in the interlayer regions and along grain surfaces.

The acid hydrolysis products of trioctahedral fluorohectorite and phlogopite have been investigated by XRD, MAS NMR spectroscopy and nitrogen BET surface area analysis in an effort to assess the relative importance of edge attack and gallery access mechanisms. A dramatic loss of X-ray crystallinity and the formation of Q3 and Q4 SiO4 sites accompanied the depletion of Mg2+ from the octahedral sheet of both 2:1 layered structures. Depending on the extent of hydrolysis, the products derived from fluorohectorite exhibited surface areas up to 208 m2/g, whereas phlogopite hydrolysis products gave values <20 m2/g. The dramatic differences in surface areas were not related to differences in hydrolysis mechanisms. 19F MAS NMR studies indicated that the hydrolysis of fluorohectorite occurred primarily by an edge attack mechanism equivalent to the hydrolysis pathway for phlogopite. A gallery access mechanism contributed to the hydrolysis of fluorohectorite only at the later stages of octahedral Mg2+ depletion. Solvation effects appeared to be important in determining the surface areas of the reaction products derived from the swelling (fluorohectorite) and non-swelling (phlogopite) precursors.

A ferrous saponite (griffithite) from Griffith Park (California, USA) was treated with solutions of HCl (0.62, 1.25 and 2.5% by weight) at 25°C for 2, 6, 24 and 48 hours. The resulting solids were characterized by XRD, FT-IR spectroscopy, thermal analyses, SEM, TEM and nitrogen adsorption isotherms at 77 K, showing the destruction of silicate structure by the treatments. The free silica generated by these treatments was digested and determined in all samples. Several samples had specific surface areas up to 250 m2/g, with maximum values which are 10 times higher than the surface area of natural saponite (35 m2/g). A sudden decrease in specific surface areas was observed when free silica was digested, which indicates that free silica makes a very important contribution to the surface area of leached samples.

Sorption parameters are important components of models used to predict mass transport through dense or compacted earthen materials. These parameters are, however, generally determined in batch tests with loose, unconsolidated materials. Here we directly measure, using a specially designed cell, the extent of Cs+ sorption on bentonite compacted to a series of densities ranging from 0.50 to 1.50 Mg/m3, and compare the results with those obtained from batch tests with loose bentonite. The clay was saturated with a Na-Ca-Cl-dominated solution with an effective ionic strength of 220 mol/m3. The sorption data were expressed as distribution coefficients, Kd. Over the clay density range examined, Kd values for Cs+ with compacted clay are about one-half to one-third the value of those with loose clay. The lower sorption on compacted clay is attributed to small and occluded pores that Cs+ cannot enter; thus it cannot access the entire volume, or all the sorption sites, of compacted clay. The data suggest that reasonable estimates of Kd with compacted clay can be obtained by scaling down the Kd values measured on loose clay by a factor na/n, where na is the accessible porosity and n the total porosity of compacted clay.

X-ray absorption fine structure (XAFS) spectra were collected on a series of ferrihydrite samples prepared over a range of precipitation and drying conditions. Analysis of the XAFS pre-edge structures shows clear evidence of the presence of lower coordination sites in the material. These sites, which are most likely tetrahedral, are believed to be at the surface and become coordination unsaturated (CUS) after dehydroxylation. With chemisorbed water molecules, the CUS sites become the crystal growth sites responsible for the phase transformation of ferrihydrite to hematite at low temperatures. On the other hand, when impurity anions such as SiO4−4 are present in the precipitation solution, the CUS sites may instead absorb the impurity anions, thereby blocking the crystal growth sites and inhibiting the formation of hematite.

A new chemical mass balance technique has been developed for simultaneous mineralogical quantification and chemical characterization of soil clays. The procedure includes separation of the whole clay (<2 μm fraction) into six particle size fractions (<0.02, <0.06, <0.2, 0.02–0.06, 0.06–0.2, and 0.2–2 μm fractions), chemical analysis of the whole clay and each of the six fractions, and fitting of a nonlinear chemical mass balance model to the chemical analyses. As written, the chemical mass balance model is valid only for samples containing mixtures of quartz, kaolinite, illite, and mixed-layered smectiteillite. Samples containing carbonates and free iron compounds may be analyzed using the technique if these phases are chemically removed prior to particle size fractionation. Accuracy of the new technique was tested using synthetic data and found to depend on the quality of the input data; however, clay phase quantification within three percentage points of known values was readily achieved. Precision of the technique was evaluated by independently preparing and analyzing five samples of the same soil clay. Standard deviations for clay phase percentages (w:w) in the <2 μm fraction were all less than one percent. The new technique yields accurate determinations of chemistry for the smectitic and illitic phases in mixed-layered smectiteillite, and qualitative estimates for the chemistry of 10 Å-illite. The elemental compositions of quartz and kaolinite are assumed a priori and treated as constants within the non-linear chemical mass balance model.

Technical limitations have restricted investigations of rhizosphere mineralogy. Various analytical techniques were applied to assess root-mineral associations and dynamics in natural soils under corn production. Soil samples were collected between four and five weeks after planting and included rhizospheric and non-rhizospheric soils, and undisturbed block samples containing corn root systems. Analytical techniques were applied and included; X-ray diffraction, optical microscope, SEM, EDXRA with SEM, transmission electron microscope (TEM), electron energy loss spectra with TEM, high-resolution transmission electron microscope (HRTEM) and microanalysis with HRTEM. The mineralogy of the rhizosphere differed from that of the bulk soil. Within the rhizosphere, minute platy particles which were mostly vermiculitic minerals, were particularly concentrated near or on root surfaces. These platy mineral particles were not attached to the entire area, but only to certain areas of root surfaces. Therefore, we report quantitative evidence for mineralogical changes in the rhizosphere in soil environments.