Peter Uhlík

Smectite-to-illite alteration in salt-bearing bentonites (the East Slovak Basin)

The effect of a saline environment on illitization in volcanoclastic rocks is examined in deep boreholes in the East Slovak Basin. Based on X-ray diffraction analysis, it is concluded that illite-smectite (I–S) expandability is always less in the salt-bearing bentonites (SBB) than in the salt-free bentonites (SFB) for a given depth interval. These two lithologies can be distinguished easily by water-leachate chemistry. Within the depth interval 2100–2500 m, the expandability in SBB varies within the range 25–10% expandable with R1 and R3 ordering in SBB and 68–35% expandable with R0 ordering in SFB. In two shallow SBB samples the expandability is close to that of SFB, suggesting that salinity alone does not enhance the illitization; but salinity may enhance it when combined with higher burial temperature. Vitrinite reflectance and Tmax of RockEval pyrolysis measured in adjacent shales confirm that the increased illitization in SBB is not due to heating and/or erosion. The model of burial and thermal history calibrated by organic maturity suggests that the same thermal history produces two different expandabilities in the two lithologies (SBB and SFB). Particle thickness measurements and K-Ar data were used to deduce the crystal growth mechanism of illitization in SBB. Whereas surface-controlled growth is typical for SFB, simultaneous nucleation and growth played a more important role in the case of SBB. The effect of a salty environment on the illitization is not yet fully understood and may have severe consequences for the utilization of bentonites as engineering barriers in radioactive waste disposal sites if salt formations used as host rocks are taken into account.

Structural Incorporation of As5+ into Hematite

Hematite (α-Fe2O3) is one of the most common iron oxides and a sink for the toxic metalloid arsenic. Arsenic can be immobilized by adsorption to the hematite surface; however, the incorporation of As in hematite was never seriously considered. In our study we present evidence that, besides adsorption, the incorporation of As into the hematite crystals can be of great relevance for As immobilization. With the coupling of nanoresolution techniques and X-ray absorption spectroscopy the presence of As (up to 1.9 wt %) within the hematite crystals could be demonstrated. The incorporated As(5+) displays a short-range order similar to angelellite-like clusters, epitaxially intergrown with hematite. Angelellite (Fe4As2O11), a triclinic iron arsenate with structural relations to hematite, can epitaxially intergrow along the (210) plane with the (0001) plane of hematite. This structural composite of hematite and angelellite-like clusters represents a new immobilization mechanism and potentially long-lasting storage facility for As(5+) by iron oxides.

Evolution of pyrophyllite particle sizes during dry grinding

Abstract The Bertaut-Warren-Averbach (BWA) technique and high-resolution transmission electron microscopy (HRTEM) were used to characterize the products of dry-ground pyrophyllite. Mean crystallite thickness and crystallite thickness distributions were measured for each sample using the BWA technique. Mean crystallite thickness decreases during the treatment with respect to grinding time and energy applied per unit mass. The BWA data were checked by HRTEM measurements and good fits were obtained for samples having small mean particle thicknesses. Samples with thicker particles could not be measured properly by HRTEM because the number of particles counted from images is statistically insufficient. The shape of the crystallite and the particle-size distribution were used to determine the mechanism of pyrophyllite particle degradation. Particles initially having a lognormal size distribution are first delaminated randomly, then some are delaminated preferentially, thereby producing polymodal thickness distributions. Finally all particles undergo delamination yielding a lognormal thickness distribution.

THICKNESS DISTRIBUTION OF ILLITE CRYSTALS IN SHALES. I: X-RAY DIFFRACTION VS. HIGH-RESOLUTION TRANSMISSION ELECTRON MICROSCOPY MEASUREMENTS

Two independent methods of crystal-size distribution analysis were compared: the Bertaut-Warren-Averbach XRD technique (MudMaster computer program) and high-resolution transmission electron microscopy (HRTEM). These techniques were used to measure thickness distributions of illite crystals (fundamental particles) from sets of illite-smectites from shales and bentonites that had expandabilities ranging from 86%S to 6%S. The illite-smectites were treated with a polymer (polyvinylopyrolidone, PVP) to separate them into fundamental particles for XRD and HRTEM investigations.A systematic difference between XRD and HRTEM results was observed: XRD (area-weighted distributions) detected a larger fraction of thick (>4 nm) and a smaller fraction of thin crystals as compared to HRTEM (number-weighted distributions). As a result, XRD-determined distributions have larger mean thickness values and larger distribution parameters (α and β2). The measurements performed by the two techniques were verified by modeling XRD patterns of the PVP-illites, using the measured distributions as inputs. The modeling indicated that the XRD-determined distributions are very accurate. Selecting broader thickness distributions in MudMaster further improved the modeling results. The HRTEM measurements underestimate the proportion of coarse particles, in particular in shale samples, and this inaccuracy is attributed to the effect of using number-weighted (rather than area-weighted) distributions and to inaccurate counting statistics for thick crystals.

High-resolution transmission electron microscopy of mixed-layer clays dispersed in PVP-10: a new technique to distinguish detrital and authigenic illitic material

Abstract The results of a new technique for the measurement of the thickness distribution of fundamental particles are reported. The technique is based on high-resolution transmission electron microscopy (HRTEM) of Na-saturated mixed-layer illite-smectite dispersed in polyvinylpyrrolidone (PVP-10). Intercalation of PVP-10 increases the spacing of expandable interlayers and changes the arrangement of particles so that the number of layers per fundamental particle can be counted easily on HRTEM images. The data obtained by HRTEM on PVP-10-intercalated illite-smectite of hydrothermal origin are compared with data from the Pt-shadowing technique. A good agreement between the two methods for the measured thickness distributions, mean thickness and expandability confirms the reliability of the new technique. The same technique is applied to a set of four sedimentary samples with different expandabilities (83-18%). The thickness of illite particles from shales and claystones has a lognormal distribution. Detrital and discrete illite particles can be distinguished from the thickness distribution of authigenic illite.

Mineral stability of Fe-rich bentonite in the Mock-Up-CZ experiment

Mineral stability of Fe-rich bentonite in the Mock-Up-CZ experiment Bentonite is a basic component of most concepts of multibarrier systems in underground radioactive waste repositories. It is important to determine the bentonite stability under the conditions close to the future real situation. The paper brings the detailed mineral and structural analyses of smectites from the bentonitic material exposed to the long term Mock-Up-CZ experiment. The compacted barrier blocks and residual filling contained 85 % of bentonite from the Rokle deposit, 10 % of quartz sand and 5 % of graphite. They were exposed to temperatures of up to 90 °C for almost 4 years. Quantitative mineral analyses, crystal size distributions, FTIR spectra, as well as cation exchange capacity and layer charge density show high mineral stability of the Rokle bentonite under the conditions of Mock-Up-CZ experiment. Small changes in the crystal sizes and slight change in the layer charge as a consequence of the experimental alteration could be linked to the hydration and the variation of the geochemical environment of the experiment.

PARTIAL DISSOLUTION OF GLAUCONITIC SAMPLES: IMPLICATIONS FOR THE METHODOLOGY OF K-Ar AND Rb-Sr DATING

The K-Ar dating of glauconite has been used as an important stratigraphic tool for many decades. The application of this technique is limited to pure glauconites, free of detrital contamination by K-bearing phases, often not easy to detect. This study extends the application of isotope dating to the contaminated glauconites and offers a precise technique for detecting the detrital contamination of glauconites.The most common K-bearing detrital contaminants have smaller (K-feldspars, Al-rich dioctahedral micas) or greater (trioctahedral micas) dissolution rates than glauconite in extremely low pH solutions. The differences in the dissolution rates can be applied to evaluate the purity of the glauconite and its crystallization age.The interlaboratory GLO glauconite standard and grain-size fractions separated from glauconitic sandstones of the Paleogene (sample GL) and Jurassic (sample GW8) ages were treated with acid (3M HCl, at 99±2°C) for different reaction times (0.5–7 h) and measured for their apparent isotopic ages.Microporous amorphous silica with large specific surface area is the solid product of the reaction and its content increases with reaction time. The K-Ar dates (apparent ages) of the solid residues increase significantly with reaction time: from 44.6 to 107 Ma for the GL sample and from 125.7 to 394.7 Ma for GW8. The increase is negligible in the case of the GLO standard. The Rb-Sr data of the GL sample were modeled using initial 87Sr/Sr ratios of 0.707–0.709, which resulted in a 29.9–35.8 Ma date for the untreated portions of GL, and ∼42.6 Ma after 7 h of treatment.The increase of isotopic K-Ar date with increasing time of dissolution is interpreted to be a result of increasing concentration of detrital, acid-resistant, K-bearing minerals, observed also with the electron microscope and X-ray diffraction. Probabilistic modeling based on single (K-Ar) or double (K-Ar and Rb-Sr) isotopic systems evaluated the isotopic ages of the detrital and authigenic minerals, and their K2O and Rb concentrations. The crystallization ages computed using these two methods are: 24.0, 26.5, and 32.3 Ma for the GL material, and 117.3–121.8 Ma for the GW8 series.The proposed method based on partial dissolution is a potential tool for evaluating the reliability of glauconite dating.

Particle properties of hydrothermal ammonium-bearing illite-smectite

Mixed-layer illite-smectite with high degree of ordering (rectorite-like clay) and with three types of interlayer cations — K+, Na+ and

INFLUENCE OF GRINDING AND SONICATION ON THE CRYSTAL STRUCTURE OF TALC

{\rm{NH}}_4^ +

XRD, SAXS, and PALS investigations of three different polymers reinforced with tetraoctylammonium exchanged montmorillonite

NH4+, was determined in the high-sulfide epithermal mineralization of the Western Carpathian Mountains. The tobelitic portion of the clay comprises 5–10%. Ammonium was detected both by chemical analysis and by Fourier transform infrared analysis. Some of the ammonium can be assigned to a poorly bound form, not fully fixed in the illitic interlayer. The finest size fraction separated from the samples behaves differently from the rest of the sample. It contains two layers of water molecules in the expandable interlayers as determined by X-ray diffraction, whereas coarser fractions have only one water layer in the interlayers.