Showing papers on "Nontronite published in 2012"

Sb(III) and Sb(V) Sorption onto Al-Rich Phases: Hydrous Al Oxide and the Clay Minerals Kaolinite KGa-1b and Oxidized and Reduced Nontronite NAu-1

Abstract: We have studied the immobilization of Sb(III) and Sb(V) by Al-rich phases - hydrous Al oxide (HAO), kaolinite (KGa-1b), and oxidized and reduced nontronite (NAu-1) - using batch experiments to determine the uptake capacity and the kinetics of adsorption and Extended X-ray Absorption Fine Structure (EXAFS) Spectroscopy to characterize the molecular environment of adsorbed Sb. Both Sb(III) and Sb(V) are adsorbed in an inner-sphere mode on the surfaces of the studied substrates. The observed adsorption geometry is mostly bidentate corner-sharing, with some monodentate complexes. The kinetics of adsorption is relatively slow (on the order of days), and equilibrium adsorption isotherms are best fit using the Freundlich model. The oxidation state of the structural Fe within nontronite affects the adsorption capacity: if the clay is reduced, the adsorption capacity of Sb(III) is slightly decreased, while Sb(V) uptake is increased significantly. This may be a result of the presence of dissolved Fe(II) in the reduced nontronite suspensions or associated with the structural rearrangements in nontronite due to reduction. These research findings indicate that Sb can be effectively immobilized by Al-rich phases. The increase in Sb(V) uptake in response to reducing structural Fe in clay can be important in natural settings since Fe-rich clays commonly go through oxidation-reduction cycles in response to changing redox conditions.

Microbial reduction of structural iron in interstratified illite‐smectite minerals by a sulfate‐reducing bacterium

Abstract: Clay minerals are ubiquitous in soils, sediments, and sedimentary rocks and could coexist with sulfate-reducing bacteria (SRB) in anoxic environments, however, the interactions of clay minerals and SRB are not well understood. The objective of this study was to understand the reduction rate and capacity of structural Fe(III) in dioctahedral clay minerals by a mesophilic SRB, Desulfovibrio vulgaris and the potential role in catalyzing smectite illitization. Bioreduction experiments were performed in batch systems, where four different clay minerals (nontronite NAu-2, mixed-layer illite-smectite RAr-1 and ISCz-1, and illite IMt-1) were exposed to D. vulgaris in a non-growth medium with and without anthraquinone-2,6-disulfonate (AQDS) and sulfate. Our results demonstrated that D. vulgaris was able to reduce structural Fe(III) in these clay minerals, and AQDS enhanced the reduction rate and extent. In the presence of AQDS, sulfate had little effect on Fe(III) bioreduction. In the absence of AQDS, sulfate increased the reduction rate and capacity, suggesting that sulfide produced during sulfate reduction reacted with the phyllosilicate Fe(III). The extent of bioreduction of structural Fe(III) in the clay minerals was positively correlated with the percentage of smectite and mineral surface area of these minerals. X-ray diffraction, and scanning and transmission electron microscopy results confirmed formation of illite after bioreduction. These data collectively showed that D. vulgaris could promote smectite illitization through reduction of structural Fe(III) in clay minerals.

Quantitative Mineralogy from Infrared Spectroscopic Data. I. Validation of Mineral Abundance and Composition Scripts at the Rocklea Channel Iron Deposit in Western Australia

Abstract: Visible-near to shortwave infrared reflectance spectra (VNIR-SWIR—400–2,500 nm wavelength region) provide quantitative measurements of mineral abundances and mineral physicochemistries from drill core samples of channel iron ore. The infrared spectral reflectance measurements of drill core samples from the Rocklea channel iron deposit, located in the Hamersley Basin of Western Australia, were validated against X-ray flouresence (XRF) and X-ray diffraction (XRD). The reflectance data were collected using a CSIRO Hy-Logging™ system from 180 reverse circulation and 14 diamond drill cores spanning a depth from surface to 55 m below surface, intersecting the Rocklea deposit. The mineralogy of this channel iron deposit comprises chiefly goethite (both vitreous and ochreous forms) with lesser amounts of hematite and variable amounts of quartz, kaolinite, smectite (both dioctahedral and trioctahedral varieties), and carbonate (both dolomite and calcite). Iron ore and waste rock mineralogy were extracted from the infrared spectroscopic reflectance data using the geometry (depth/wavelength) of continuum-removed reflectance spectra, with depths of absorption features proportional to mineral abundance and wavelength positions proportional to chemical composition. For any one mineral, a number of its diagnostic spectral features are used to determine its mineral abundance and composition, in order to avoid complications with minerals that spectrally overlap with part of the diagnostic spectral features of the mineral of interest. This method that combines multiple spectral features to identify and quantify minerals is transferable to all types of infrared reflectance spectroscopic data collected from drill core to satellites. Final products include: iron (oxyhydr-)oxide content (root mean square error (RMSE) 9.1 wt % Fe); Al clay content (RMSE 3.9 wt % Al 2 O 3 ); hematite/goethite ratio (RMSE 9.0 wt % goethite); vitreous versus ochreous goethite (not easily measured using other analytical techniques); clay mineral type (kaolinite, montmorillonite and nontronite); and carbonate composition (dolomite vs. calcite). The Rocklea infrared reflectance spectroscopy-based mineral abundance and composition results have been used in an associated study to characterize the architecture of the Rocklea channel iron deposit, with implications for exploration, mining, and ore genesis.

Mineralogical and Physico-Chemical Characterizations of Ferruginous Beidellite-Rich Clay from Agadir Basin (Morocco)

Abstract: The mechanism of formation of detrital, beidellite-rich clay occurring in the Agadir basin (Morocco) is well documented, but its detailed characterization is incomplete which limits its application. The aim of the present study was to provide further details of the mineralogical and physico-chemical characteristics of this clay. Bulk raw clay and its Na+-saturated, <2 mm fraction were characterized using chemical, structural, and thermal techniques. Measurements of induced streaming potential (e.g. particle charge) and of specific surface area and porous volume are reported. The raw clay contained carbonate and quartz as associated minerals along with phyllosilicates (<2 mm particle size). X-ray diffraction and scanning electron microscopy analyses showed that the <2 mm fraction was dominated by a dioctahedral smectite. Because dehydroxylation of this mineral occurred at 510oC, and because it re-expanded in ethylene glycol after Li+-saturation followed by heating at 240oC for 24 h, the mineral was shown to be a beidellite rather than montmorillonite. This assertion was further supported by 27Al and 29Si magic-angle spinning nuclear magnetic resonance spectra showing predominantly negative charges in the tetrahedral sheets due to notable Al-for-Si substitutions. The chemical composition of the <2 mm fraction showed an Fe2O3 content which was ~7.52 wt.% greater than those of other beidellite occurrences but not so much that it would be identified as a nontronite. The absence of stretching and bending absorption bands corresponding to characteristic (Fe2OH) units in mid-infrared spectra and their corresponding fundamental overtones or combination bands in near-infrared spectra supported this notion. The structural formula of the beidellite in the present study was determined to be (Si7.51Al0.49)(Al2.99Fe0.68Mg0.33) (Ca0.03Na0.54Mg0.11)O20(OH)4, having dioctahedral ferruginous characteristics with almost 60% of the negative charge found in tetrahedral sheets. The cation exchange capacity determined from the structural formula was ~108 meq/100 g. The specific surface area and total pore volume were ~82.2 m2/g and 0.136 cm3/g, respectively. Interestingly, a detrital rather than a hydrothermal-alteration origin, as reported for other beidellite occurrences, explains its natural abundance and emphasizes the great interest in it.

Rehydration of dehydrated-dehydroxylated smectite in a low water vapor environment

Abstract: Thermal analysis experiments in the environment of an extremely low water vapor concentration provide insight into the first steps of the rehydration mechanism in smectite when completely dehydrated and the interlayer region is collapsed. The relative structural and compositional controls on dehydration and rehydration reactions are compared from a well-characterized suite of samples that vary with respect to chemical composition, octahedral and tetrahedral substitution, octahedral cation site vacancy, and degree of dehydroxylation. Techniques including multi-cycle heating-cooling thermogravimetric analysis and nitrogen gas adsorption on various smectite samples preheated at different temperatures followed by rehydration at ambient conditions were used to characterize the interaction of water molecules with completely dehydrated montmorillonite, beidellite, and nontronite smectite types. Beidellite with high-Al 3+ tetrahedral substitution results in electrostatically undersaturated basal oxygen atoms that exert strong repulsion between the tetrahedral sheets of adjacent 2:1 layers. The interlayer region of dehydrated or dehydroxylated beidellite is capable of being spontaneously rehydrated even in low water vapor environments. In completely dehydrated montmorillonite and nontronite, the external surface area of the crystallites is a primary control on water adsorption at low humidity when the molecules form a shell around the exchangeable cations present on external surfaces. The potential of montmorillonite and nontronite to reopen a collapsed interlayer is significantly lower than beidellite because of their crystal-chemical features that result in 2:1 layer and interlayer cation attraction. With increasing water vapor partial pressure, the hydration potential of interlayer cations provokes a reopening of the interlayer. In a dehydroxylated nontronite, the undersaturated residual oxygen atom strongly bonds the interlayer cation within the ditrigonal ring of the tetrahedral sheet, resulting in a permanent interlayer collapse. The specific surface area calculated from a conventional N 2 gas adsorption measurement using the BET model represents the external surface area of a dehydrated smectite crystallite and can be converted into the mean crystallite thickness. The mean crystallite thickness of a completely dehydrated smectite increases with an increase in preheating temperature.

Evolution with depth from detrital to authigenic smectites in sediments from AND-2A drill core (McMurdo Sound, Antarctica)

Abstract: We have examined the nature and origin of smectites in glaciomarine sediments of the AND-2A drill core (McMurdo Sound, Antarctica) by means of X-ray diffraction (XRD) analyses on the clay fraction, field emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM) observations and SEM-EDS microanalyses on smectite particles. Relying on the smectite variation throughout the drill core it was possible to split the sequence into three units. Smectites throughout the core are either detrital or authigenic. Detrital smectites are close to montmorillonite-beidellite in composition while newly-formed smectites frequently have higher Fe-Mg contents and intermediate compositions between the saponite and nontronite field, with lower amounts in the montmorillonite-beidellite field. In the upper sedimen tary sections (Unit I, and Unit II, 36–440 mbsf, 0.7–16.5 Ma) smectites are interpreted to be predominantly detrital, whereas in the lower portion of the core (Unit III, 440–1123.20 mbsf, 16.5–20.2 Ma) authigenic smectites are the most common feature. The predominance of mica, the abundance of chlorite, and the nature of smectites in the upper units indicate physical weathering under cold and dry climate, and a dominant provenance for the clay minerals from the Transantarctic Mountains. Smectites in the lower unit are considered mostly authigenic and they are most likely to be the result of early diagenetic processes, being formed from the alteration of volcanic material (glass, pyroxenes and feldspars) and/or through precipitation from fluids of a possible hydrothermal origin. Our survey attests to the importance of discrimi nating between a detrital and authigenic nature of smectites as the occurrence of authigenic clay minerals in ancient sedimentary successions might lead to incorrect paleoclimatic interpretations, since they can be affected by diagenetic processes, thus obliterating the climatic signal.

Nature of rehydroxylation in dioctahedral 2:1 layer clay minerals

Abstract: Rehydroxylation of the previously dehydroxylated dioctahedral 2:1 layer clay mineral occurs preferentially in specific sites within the former octahedral sheet. The rehydroxylation of dehydroxylated Al-rich and Al,Mg-rich 2:1 layers occurs as trans -vacant ( tv ) structural arrangements, regardless of whether the initial structure was tv or cis -vacant ( cv ). In nontronite (Fe-rich 2:1 layer clay), the dehydroxylate pseudo-cv structure is probably directly reconstructed into the rehydroxylated cv structure without migration of octahedral cations. Rehydroxylation occurs preferentially in the R 3+ -O r -R 3+ former octahedral structural arrangements (O r = residual oxygen) over R 2+ -O r -R (R = R 3+ or R 2+ = Al 3+ , Fe 3+ or Mg 2+ , Fe 2+ ). In the case of the R 2+ octahedral substitution, the interlayer cation is attracted to the electrostatically undersaturated residual oxygen of the R 2+ -O r -R arrangement, which blocks the ability of water molecules to pass through the ditrigonal cavity and rehydroxylate the previously dehydroxylated local arrangement. The pyrophyllite-like type of octahedral R 3+ -O r -R 3+ arrangements, formed due to the lack of tetrahedral substitution and resulting in the absence of interlayer cations, is thus favored for rehydroxylation over the mica-like R 3+ -O r -R 3+ arrangements where Al occurs in the tetrahedral sheet. The valence of the interlayer cation and the charge density of the 2:1 layer clay mineral, which controls the interlayer cation content, also affect the degree of rehydroxylation. Dehydroxylated 2:1 layer minerals with a high-rehydroxylation potential, including beidellite and illite, use all the adsorbed water molecules that persist above 200 °C for rehydroxylation; the water vapor from the ambient environment also becomes a source of H 2 O molecules for rehydroxylation. The high demand for water molecules to use for rehydroxyltion results in a noticeable gain of mass in the temperature interval between 200 and 350 °C even during heating.

Desorption and Transformation of Nitroaromatic (TNT) and Nitramine (RDX and HMX) Explosive Residues on Detonated Pure Mineral Phases

Abstract: Explosive compounds, including known toxicants 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), are loaded to soils during military training. Their fate in soils is ultimately controlled by soil mineralogical and biogeochemical processes. We detonated pure mineral phases with Composition B, a mixture of TNT and RDX, and investigated the fate of detonation residues in aqueous slurries constructed from the detonated minerals. The pure minerals included Ottawa sand (quartz and calcite), microcline feldspar, phlogopite mica, muscovite mica, vermiculite clay, beidellite (a representative of the smectite clay group), and nontronite clay. Energy-dispersive X-ray spectrometry, X-ray diffraction, and gas adsorption surface area measurements were made of the pristine and detonated minerals. Batch slurries of detonated minerals and deionized water were sampled for 141 days and TNT, RDX, and TNT transformation products were measured from the aqueous samples and from the mineral substrates at day 141. Detonated samples generally exhibited lower gas adsorption surface areas than pristine ones, likely from residue coating, shock-induced compaction, sintering, and/or partial fusion. TNT and RDX exhibited analyte loss in almost all batch solutions over time but loss was greater in vermiculite, beidellite, and phlogopite than in muscovite and quartz. This suggests common phyllosilicate mineral substrates could be used on military training ranges to minimize off-site migration of explosive residues. We present a conceptual model to represent the physical and chemical processes that occurred in our aqueous batches over time.

Composition and method for removing metal contaminants

Abstract: A composition comprising a substrate, an organic ion, and a metal binding agent, wherein the substrate comprises a natural clay, a synthetic clay, a natural zeolite, a synthetic zeolite, a polymer resin, lignite, kaolinite, serpentine, illite, chlorite, smectite, montmorillonite, saponite, sepiolite, nontronite, beidellite, hectorite, fuller's earth, attapulgite, bentonite, analcime, chabazite, heulandite, natrolite, phillipsite, stilbite, diethyl aminoethyl, quaternary aminoethyl, or combinations thereof, wherein the organic ion comprises quaternary amines, imidazolium salts, phosphonium salts, tetra alkyl ammonium, bis-(hydrogenated tallow)-dimethyl-ammonium chloride, bis-(hydrogenated tallow)-benzyl-methyl-ammonium chloride, 4,5-dihydro-1-methyl-2-nortallow-alkyl-1-(2-tallow-amidoethyl)-imidazolium methyl sulfate, 1-ethyl-4,5-dihydro-3-(2-hydroxyethyl)-2-(8-heptadecenyl)-imidazolium ethyl sulfate, or combinations thereof, and wherein the metal-binding agent comprises mercaptan, carboxylic acid, chelating agents, amines, esters, carboxylic acids, alcohols, ethers, aldehydes, ketones, alkenes, alkynes, mercaptans, thiols, tert-dodecanethiol, nonanethiol, octanethiol, n-stearic acid, iso-stearic acid, palmitic acid, or combinations thereof.

Characterization of Alteration Phases on HLW Glasses After 15 Years of PCT Leaching

Abstract: We have collected an extensive data base of leaching data for numerous high-level nuclear waste (HLW) glass compositions using the PCT leaching procedure (deionized water, 90°C, S/V = 2000 m -1 ) for test durations of up to fifteen years. In a previous paper, statistical tools were used to evaluate the solution data and to classify several qualitatively different types of leaching behavior. In particular, it was found that there is a clear segregation between glasses with alteration rates that remain low and those that show resumptions of alteration. In this paper, we focus on the surface characterization of samples of leached glass recovered from these tests. From the subset of 98 glass compositions used in the development of the reference glass formulation for the immobilization of West-Valley nuclear waste, leached samples of 22 glasses were characterized. When no resumption of alteration occurs, the residual rate is approximately constant and non-zero. The existence of a residual rate appears to be linked to the slow growth of a phyllosilicate (smectite-type) phase containing Fe, Mg, and K. A nontronite phase is identified by XRD while SEM-EDS gives an average composition of (Na,K) 0.8 (Fe,Mg) 1.3 (Al,Si) 4 O 10 . The occurrence of a resumption of alteration is associated with the precipitation of zeolite-type aluminosilicate phases, identified by XRD as phillipsite, with a typical composition (K,Na,Ca 0.5 ) 1-2 (Si, Al) 8 O 16 .6H 2 O, as measured by SEM-EDS. In such cases, the glass is still covered with the underlying nontronite phase of the same average composition as identified for samples that have not exhibited a rate increase. Both our earlier evaluation of the leachate concentrations and the present results from characterization of the alteration phases highlight the important effects of the glass composition, to the extent of producing qualitatively different alteration behavior.

Quantitative analysis of turbostratically disordered nontronite with a supercell model calibrated by the PONKCS method

Abstract: Two calibration-based quantitative X-ray diffraction (XRD) models for turbostratically disordered Bulong nontronite, the PONKCS (partial or no known crystal structure) approach and the supercell structural model, were compared in terms of the accuracy and refinement error from Rietveld quantitative phase analysis. The PONKCS approach achieved improved nontronite quantitative results with synchrotron diffraction patterns compared with those achieved with laboratory XRD data as a result of better data quality and the use of Debye–Scherrer geometry with significantly reduced preferred orientation effects. The introduction of a peak shape modifier (spherical harmonics) to correct the quantification result is mainly useful for laboratory XRD patterns containing nontronite collected from Bragg–Brentano geometry with appreciable preferred orientation effects. A novel calibration approach for the nontronite supercell model was developed, based on the Rietveld quantitative formula in the TOPAS symbolic computation system. The calibrated supercell model achieved better accuracy (deviation within 1 wt%) and lower refinement error than the PONKCS approach because the physically based description of turbostratic disorder requires fewer refinable parameters than the PONKCS approach. The drawbacks and limitations of the supercell approach are also discussed.

A method of adsorbing and immobillizing heavy metals in contaminated soil using modified clays and phosphates

Abstract: PURPOSE: A method for adsorbing and immobilizing heavy metal polluted soil using modified clay and a phosphate-based compound is provided to improve the eliminating effect of heavy metals by eliminating heavy metals from polluted soil and immobilizing the heavy metals. CONSTITUTION: Heavy metals are eliminated from polluted soil by mixing modified clay and the polluted soil. The modified clay is modified with iron oxide or manganese oxide. A phosphate-based compound is further used with the modified clay. The clay is diatomate, montmorillonite, bentonite, zeolite, smectite, phyllosilicate, saponite, beidellite, nontronite, vermiculite, kaolinite, halloysite, mica, muscovite, paragonite, dickite, nacrite, halloysite, antigorite, chrysotile, hectorite, clintonite, donbassite, cookeite, silica, or the combination of the same. The phosphate-based compound is diammonium phosphate, hydroxyapatite, waste phosphoric acid, K_3PO_4, K_2PO_4, KH_2PO_4, CaHPO_4, FeH_2PO_4, FeHPO_4, AlH_2PO_4, Na_2HPO_4, NaH_2PO_4, or the combination of the same.

Study of nanocrystals in the dynamic slip zone

Abstract: Mineral composition is studied and a search to detect nanocrystals is conducted in the surface layers of slickensides formed due to dynamic slip in arkose sandstone. The infrared and Raman spectroscopy show that the slickensided layer is composed of nanocrystals of montmorillonite and anatase measuring ≈15 nm and 3 nm, respectively. The crystalline lattice of the nanocrystals of montmorillonite is stretched by ≈2.5% while the lattice of the nanocrystals of anatase is compressed by ≈0.12%. Deeper than 3 mm below the slickenside surface, the sandstone contains nanocrystals of montmorillonite, beidellite and nontronite, quartz, plagioclase, and anatase. The nanocrystals of anatase have a linear size of ≈8 nm. Their crystalline lattice is compressed by ≈0.03%. It is supposed that montmorillonite in the slickensides was formed due to hydrolytic decomposition of silicates under friction of the fault planes sliding past each other.

Water sorption in hybrid silica gels containing colloidal nontronite

Abstract: Hybrid silica gels (HSGs) were prepared according to an acid-catalyzed sol–gel method using tetraethoxysilane (TEOS) as silica precursors and colloidal suspension of nontronite clay mineral. The silica surfaces were hydrophilic in relation to silanol groups and it was of interest to increase hydrophobicity by substituting silanol by methylated groups through addition of methyltrimethoxysilane (MTMS) in a molar ratio TEOS: MTMS equaled to 1:0.4. The aim of the present paper was to predict effects of water content in soil on HSG hydration by characterizing HSG water desorption and sorption with dynamic vapor sorption device. From desorption kinetics, TEOS HSGs showed higher ability to water surface evaporation and diffusion compared to the TEOS–MTMS HSGs. After complete dehydration, water sorption isotherms Type II were obtained for HSGs. Isotherms were fitted with Brunauer-Emmett-Tellet (BET) and Guggenheim, Andersen, de Boer (GAB) models. The higher monolayer values of water adsorbed for HSGs containing nontronite suggested a major influence of clay minerals on overall hydration. However, the water binding energy depended upon the nature of silica matrix indicating weaker bonds with methylated groups at solid surface in MTMS–TEOS HSGs. Apparent water sorption diffusivities, Dapp were calculated according to Fick’s diffusion model. Maximal Dapp values were obtained in the range 0.2–0.3 aw after which the Dapp decreased in relation with capillary condensation.

Mineralogical and micromorphological characteristics of Si-Fe-Mn oxyhydroxides from the PACMANUS hydrothermal field, Eastern Manus Basin

Abstract: The mineralogical and micromorphological characteristics of Si-Fe-Mn oxyhydroxides from the dacite-hosted PACMANUS hydrothermal field were analyzed. The samples are poorly crystallized Si-Fe-Mn oxyhydroxides with minor birnessite, todorokite, nontronite, goethite, and opal-A. There are some microtextures which are rather like fossil microbes such as the filamentous silica and the hollow pipes. Flakes of nontronite crystals are found either forming a honeycomb texture or distributed on the surface of the hollow pipes. Nontronite is the product precipitated from low-temperature hydrothermal fluids, and microbes may play a role in its formation. Si-Fe-Mn oxyhydroxides have two kinds of nuclei: Si-Mn nuclei and Si nuclei, both enveloped by the similar Si-Fe outer layer, existing in the rod-shaped oxyhydroxide and spheroidal oxyhydroxide, respectively. In the Si-Mn nuclei, the concentration of SiO2 is between 39.32 wt% and 86.31 wt%, and MnO concentration is between 4.97 wt% and 27.01 wt%, but Fe2O3 concentration is very low (0.54 wt%–3.43 wt%). In the Si nucleus the concentration of SiO2 is 90.17 wt%, but concentration of MnO and Fe2O3 are low, with 0.06 wt% and 3.47 wt%, respectively. The formation of the Si-Mn nucleus is closely related to microbes, whereas the Si nucleus is of inorganic origin.

Characterization of mineral phases of agricultural soil samples of Colombian coffee using Mössbauer spectroscopy and X-ray diffraction

Abstract: Soil chemical analysis, X-ray diffraction (XRD) and Mossbauer spectrometry (MS) of 57Fe were used to characterize mineral phases of samples taken from the productive layer (horizon A) of agricultural coffee soil from Tolima (Colombia). Chemical analysis shows the chemical and textural parameters of samples from two different regions of Tolima, i.e., Ibague and Santa Isabel. By XRD phases like illite (I), andesine (A) and quartz (Q) in both samples were identified. The quantity of these phases is different for the two samples. The MS spectra taken at room temperature were adjusted by using five doublets, three of them associated to Fe + 3 type sites and the other two to Fe + 2 type sites. According to their isomer shift and quadrupole splitting the presence of phases like illite (detected by DRX), nontronite and biotite (not detected by XRD) can be postulated.

Potassium fixation by oxidized and reduced forms of different phyllosilicates

Abstract: Factors governing potassium fixation and release are poorly understood. This study was conducted to investigate the effects of clay mineralogy and structural iron oxidation state on potassium fixation. Five reference clays and two soil clays were used to capture a range in mineralogical compositions and potassium behaviors. Reference clays used were illite (IMt-1), kaolinite (KGa-1b), montmorillonite (STx-1b), nontronite (NAu-2), and vermiculite (VTx-1). Soil clays used were from the upper 15 cm of a Belvue loam (BEL) and a Cherokee silt (CHE). Potassium fixation capacities were measured on unaltered as well as sodium dithionite reduced forms of each clay. Ferrous and total iron contents were determined photometrically using 1, 10phenanthroline. Potassium fixation was measured by potassium saturating the clays and washing off exchangeable and solution potassium with solutions of magnesium chloride; samples were then acid digested and the amount fixed was calculated as the amount of potassium in the acid digestion minus the amount originally in the sample. BEL released potassium rather than fixed it while CHE tended to release potassium in the unaltered form and fix potassium in the reduced form. Structural iron reduction significantly impacted the amounts of potassium fixed by VTx-1 and NAu-2, which had the highest total iron contents of all the clays evaluated. NAu-2 and VTx1 both on average fixed less than 1 mg K g clay -1 in the unaltered form and an average of 6 and 11 mg K g clay -1 , respectively, in the reduced form. Regardless of being in the unaltered or reduced form, KGa-1b fixed essentially no potassium and IMt-1 and STx-1b fixed intermediate amounts of potassium—2 to 4 mg K g clay -1 on average. The effects of clay mineralogy and structural iron oxidation state on potassium fixation can largely be explained through an understanding of layer type, layer charge, and charge distribution. In order for potassium fixation to occur, interlayer sites need to be accessible and available. Generally, the greater the negative layer charge the greater the amounts of fixation, with tetrahedral layer charge favoring fixation more than octahedral layer charge, and layer charge being a function of structural iron oxidation state.

Speciation of Smectites in two Shrink-swell Soils of Central Peninsular India

Abstract: Shrink-swell (Vertisols and their intergrades) soils cover an extensive area especially in Peninsular India with smectites as the dominant mineral. It was felt necessary to find out the species of smectites for better management of these soils. Hence, two benchmark Vertisols namely Seloo from Wardha and Saikhindi from Ahmadnagar districts of Maharashtra were chosen for the study. High resolution mineralogical analysis employed through X ray diffraction (XRD) techniques of the silt, total clay and fine clay fractions of both the pedons were carried out along with Greene-Kelly test with only fine clays. Silt (50-2 μm), total clay (<2 μm) and fine clay (<0.2 μm) fractions are dominated by smectite in both the soils; the smectites content increased gradually with decreasing size fraction. The fine clay fractions are mostly composed of smectite with small amounts of vermiculite and traces of chlorite, kaolin and feldspar. Greene-Kelly test indicated that both Seloo and Saikhindi soil fine clays are dominated by beidellite/nontronite over montmorillonite. The Seloo fine clay smectite is composed of 18–26 per cent and 74–82 per cent montmorillonite and beidellite/nontronite, respectively, and for Saikhindi it is composed of 32–41 per cent and 59–68 per cent for montmorillonite and beidellite/nontronite, respectively. However, these fine clay smectites are of low charge dioctahedral nature and therefore may not have any K selectivity. This property appears to have implications in K management of shrink-swell soils of Deccan basalt areas.

Hydrologic and Geochemical Controls on Nontronite Formation in Terrestrial Columbia River Basalts and Implications for Clay Formation on Mars

Abstract: TERRESTRIAL COLUMBIA RIVER BASALTS AND IMPLICATIONS FOR CLAY FORMATION ON MARS. L. L. Baker, 1,2 D. G. Strawn 1 , P. A. McDaniel 1 , J. P. Fairley 2 , and J. L. Bishop 3 , 1 Division of Soil and Land Resources, University of Idaho, Moscow, ID 83844-2339, lbaker@uidaho.edu, 2 Department of Geological Sciences, University of Idaho, Moscow, ID 83844-3022, 3 Carl Sagan Center, SETI Institute & NASA-ARC, 189 Bernardo Avenue, Mountain View, CA 94043.

Laboratory-Simulated Diagenesis of Nontronite

Abstract: Nontronite NAu-1 was exposed to moderate temperature and pressure conditions (250 and 300°C at 100 MPa pressure) in KCl brine to simulate burial diagenetic systems over accelerated time periods appropriate for laboratory experiments. Powder X-ray diffraction and transmission electron microscopy analysis of the coexisting mixed-layer and discrete 10 A clay reaction products, and inductively coupled plasma-mass spectrometry analysis of the remaining fluids, indicated that the clay retained octahedral Fe and was identified as Fe-celadonite. The release of Fe from smectite during burial diagenesis has been hypothesized as a mechanism for magnetite authigenesis. High Al activity relative to Fe may be critical to the formation of an aluminous illite and any associated authigenic magnetite.

Quantitative Determination of Fe-oxidation State by Electron Energy Loss Spectroscopy (EELS)

Abstract: The consequences of microbe-mineral interaction often resulted in the chemical, structural modification, or both in the biologically induced mineral. It is inevitable to utilize the high powered resolution of electron microscopy to investigate the mechanism of biogenic mineral transformation at nano-scale. The applications of transmission electron microscopy (TEM) capable of electron energy loss spectroscopy (EELS) to the study of microbe-mineral interaction were demonstrated for two examples: 1) biogenic illite formation associated with structural Fe(III) reduction in nontronite by Fereducing bacteria; 2) siderite phase formation induced by microbial Fe(III) reduction in magnetite. In particular, quantification of the changes in Fe-oxidation state at nanoscale is essential to understand the dynamic modification of minerals resulted from microbial Fe reduction. The procedure of EELS acquisition and advantages of EELS techniques were discussed.

Stability of Mg-sulphate minerals in the presence of smectites: Possible mineralogical controls on H2O and nutrient cycling on Mars

Abstract: Hydrated sulphate minerals, including kieserite (MgSO4·H2O), gypsum (CaSO4·2H2O), and bassanite (CaSO4·~0.5H2O), have been detected on Mars (Gendrin et al., 2005; Wray et al., 2010), and polyhydrated Mg-sulphate minerals such as epsomite (MgSO4·7H2O) and meridianite (MgSO4·11H2O) may be common near the surface of the planet. Kieserite, gypsum, and bassanite have all been identified in close association with phyllosilicate minerals (most likely Fe-rich smectites such as nontronite) at the surface of Mars (Wiseman et al., 2008; Milliken et al., 2010; Roach et al., 2010; Wray et al., 2010). Layered sedimentary deposits at Gale Crater, the landing site for the Mars Science Laboratory mission, appear to contain polyhydrated Mg-sulphate minerals, kieserite, and Ferich smectite in close association (Milliken et al., 2010).