Bruno Lanson

Bio: Bruno Lanson is an academic researcher from University of Savoy. The author has contributed to research in topics: Illite & Birnessite. The author has an hindex of 47, co-authored 112 publications receiving 7241 citations. Previous affiliations of Bruno Lanson include École Normale Supérieure & Joseph Fourier University.

Investigation of smectite hydration properties by modeling experimental X-ray diffraction patterns: Part I. Montmorillonite hydration properties

Abstract: Hydration of the <1 μm size fraction of SWy-1 source clay (low-charge montmorillonite) was studied by modeling of X-ray diffraction (XRD) patterns recorded under controlled relative humidity (RH) conditions on Li-, Na-, K-, Mg-, Ca-, and Sr-saturated specimens. The quantitative description of smectite hydration, based on the relative proportions of different layer types derived from the fitting of experimental XRD patterns, was consistent with previous reports of smectite hydration. However, the coexistence of smectite layer types exhibiting contrasting hydration states was systematically observed, and heterogeneity rather than homogeneity seems to be the rule for smectite hydration. This heterogeneity can be characterized qualitatively using the standard deviation of the departure from rationality of the 00 l reflection series (ξ), which is systematically larger than 0.4 A when the prevailing layer type accounts for ~70% or less of the total layers (~25% of XRD patterns examined). In addition, hydration heterogeneities are not distributed randomly within smectite crystallites, and models describing these complex structures involve two distinct contributions, each containing different layer types that are interstratifed randomly. As a result, the different layer types are partially segregated in the sample. However, these two contributions do not imply the actual presence of two populations of particles in the sample. XRD profile modeling also has allowed the refinement of structural parameters, such as the location of interlayer species and the layer thickness corresponding to the different layer types, for all interlayer cations and RH values. From the observed dependence of the latter parameter on the cation ionic potential ( v / r; v = cation valency and r = ionic radius) and on RH, the following equations were derived: \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[Layer\ thickness\ (1W)\ =\ 12.556\ +\ 0.3525\ {\times}\ ({ u}/\mathit{r}\ {-}\ 0.241)\ {\times}\ ({ u}\ {\times}\ RH\ {-}\ 0.979)\] \end{document} \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[Layer\ thickness\ (2W)\ =\ 15.592\ +\ 0.6472\ {\times}\ ({ u}/\mathit{r}\ {-}\ 0.839)\ {\times}\ ({ u}\ {\times}\ RH\ {-}\ 1.412)\] \end{document} which allow the quantification of the increase of layer thickness with increasing RH for both 1W (one water) and 2W (two water) layers. In addition, for 2W layers, interlayer H2O molecules are probably distributed as a unique plane on each side of the central interlayer cation. This plane of H2O molecules is located at ~1.20 A from the central interlayer cation along the c* axis.

Structural model for the biogenic Mn oxide produced by Pseudomonas putida

Abstract: X-ray diffraction (XRD) and Mn K-edge extended X-ray absorption Þ ne structure (EXAFS) spectroscopy were combined to elaborate a structural model for phyllomanganates (layer-type Mn oxides) lacking 3D ordering (turbostratic stacking). These techniques were applied to a sample produced by a common soil and freshwater bacterium (Pseudomonas putida), and to two synthetic analogs, δ-MnO2 and acid birnessite, obtained by the reduction of potassium permanganate with MnCl2 and HCl, respectively. To interpret the diffraction and spectroscopic data, we applied an XRD simulation technique utilized previously for well-crystallized birnessite varieties, complementing this approach with single-scattering-path simulations of the Mn K-edge EXAFS spectra. Our structural analyses revealed that all three Mn oxides have an hexagonal layer symmetry with layers comprising edgesharing Mn 4+ O6 octahedra and cation vacancies, but no layer Mn 3+ O6 octahedra. The proportion of cation vacancies in the layers ranged from 6 to 17%, these vacancies being charge-compensated in the interlayer by protons, alkali metals, and Mn atoms, in amounts that vary with the phyllomanganate species and synthesis medium. Both vacancies and interlayer Mn were most abundant in the biogenic oxide. The diffracting crystallites contained three to six randomly stacked layers and have coherent scattering domains of 19–42 A in the c* direction, and of 60–85 A in the a-b plane. Thus, the Mn oxides investigated here are nanoparticles that bear signiÞ cant permanent structural charge resulting from cation layer vacancies and variable surface charge from unsaturated O atoms at layer edges.

Authigenic kaolin and illitic minerals during burial diagenesis of sandstones: a review

Abstract: The diagenetic evolution of kaolin and illitic minerals in sandstones is described here. The structural characterization of these minerals, the possible reaction pathways leading to their crystallization, and the origin of the fluids involved are discussed specifically. While early precipitation of kaolinite is in general related to flushing by meteoric waters, subsequent diagenetic kaolinite-to-dickite transformation probably results from invasion by acidic fluids of organic origin. Dickite is the stable polytype in most sandstone formations and the kaolinite-to-dickite conversion is kinetically controlled. The conventional model of kaolin illitization, assuming a thermodynamic control in a closed system, is discussed and compared to an alternative model in which illitization of kaolin is not coupled to dissolution of K-feldspar (Berger et al. , 1997). In the latter model, illite crystallization at the expense of kaolin implies that an energy barrier is overcome either by an increased K+/H+ activity ratio in solution or by a considerable temperature increase.

Quantitative zn speciation in smelter-contaminated soils by exafs spectroscopy

Abstract: More than a century of non-ferrous metallurgical activities have had a severe impact on the natural environment leading, in most heavily contaminated sites, to a complete loss of the vegetation cover (that is, desert-like areas) or to the selection of metal-hyperaccumulator plant species. Identifying the chemical forms of toxic metals is of vital importance for a realistic assessment of the chemical risk posed by their presence in soils and selecting effective remedia- tion technologies. In this study, X-ray diffraction (XRD), X-ray texture goniom- etry, and powder and polarized extended X-ray absorption fine structure (EXAFS, P-EXAFS) have been used to investigate quantitatively the speciation of Zn in soils contaminated by three smelters from northern France and Belgium, and coupled synchrotron-based micro-X-ray radiation fluorescence (SXRF) and mi- cro-EXAFS (EXAFS) were also used for one of these soils. Of these techniques, the application of P-EXAFS and EXAFS to molecular environmental science was unprecedented, and we show that their complementarity greatly improves the sensitivity of powder EXAFS to identify the nature of metal-containing minerals in soils. Franklinite (ZnFe2O4), willemite (Zn2SiO4), hemimorphite (Zn4Si2O7(OH)2 ·H 2O), and Zn-containing magnetite ((Fe,Zn)Fe2O4) were identi- fied in dense soil fractions by XRD and powder EXAFS. These primary minerals originate from atmospheric fallout of Zn dusts emitted during the pyrometallurgi- cal smelting process, and they act as the main source of Zn in contaminated soils. In all soil samples, Zn released in solution during the weathering of these high-temperature minerals is taken up partly by phyllosilicates and, to a lesser extent, by Mn and Fe (oxyhydr) oxides. Zn-containing phyllosilicates were identi- fied by comparing powder EXAFS spectra to a library of model compounds and from the noteworthy angular dependence of EXAFS spectra collected on self- supporting films of clay soil fractions. Analysis of higher correlations in EXAFS spectra suggests that the local structure around Zn in phyllosilicates is trioctahe- dral. The phyllomanganate Zn-sorbed birnessite and Zn-containing Fe grains having a FeOOH-like local structure were unambiguously identified bySXRF— EXAFS. In birnessite Zn is sorbed in the interlayer space above/below vacant sites and can be either 4-fold or 6-fold coordinated depending, presumably, on the anionic stacking of birnessite layers. Based on this micro-mineralogical investiga- tion, a satisfactory fit of the three identified Zn species (that is, phyllosilicate, Mn, and Fe (oxyhydr)oxides) to experimental powder EXAFS spectra of all clay soil fractions was obtained. The significance, origin, and stability of Zn-phyllosilicates are discussed. Specifically, we show that the formation of Zn-containing phyllosili- cates is consistent with calculated thermodynamic solubilities. For the range of measured Zn 2 (D10 ppm), Si(OH)4 (10-20 ppm), and H (5.6 F pH F 7.5) concen- trations, soil solutions are supersaturated (pH G 6) or near saturation (pH F 6) with respect to the trioctahedral Zn phyllosilicate, Zn-kerolite. Finally, the plausi- bility of the formation of (Zn,Al) hydrotalcite-like species contemplated by Julliot (1999) is critically assessed.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

X-Ray Diffraction

Abstract: Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.