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At least 145 records · Page 8Linked to original sources
USGS2024

Studies of the Reactivity of the Ferrihydrite Surface by Iron Isotopic Exchange and Mössbauer Spectroscopy

Two-line ferrihydrite is an important adsorbent of many toxics in natural and anthropogenic systems; however, the specific structural sites responsible for the high adsorption capacity are not well understood. A combination of chemical and spectroscopic techniques have been employed in this study to gain further insight into the structural nature of sites at the ferrihydrite surface. The kinetics of iron isotopic exchange demonstrated that there are at least two types of iron sites in ferrihydrite. One population of sites, referred to as labile sites, approached iron isotopic equilibrium within 24 hr in 59 Fe-NTA solutions, while the second population of sites, referred to as non-labile , exhibited a much slower rate of isotopic exchange. Adsorbed arsenate reduced the degree of exchange by labile sites, indicating that the anion blocked or greatly inhibited the rate of exchange of these sites. Mössbauer spectra were collected from a variety of samples including 56 Fe-ferrihydrite samples with 57 Fe in labile sites, samples containing 57 Fe throughout the structure, and samples with 57 Fe in non-labile sites. The spectra showed characteristic broad doublets signifying poor structural order. Refined fits of the spectra indicated that labile sites have larger quadrupole splitting, hence more local distortion, than non-labile sites. In all cases, the spectra demonstrated some degree of asymmetry, indicating a distribution of Fe environments in ferrihydrite. Overall spectral findings, combined with recent EXAFS results (Waychunas et al. , 1993), indicate that labile sites likely are more reactive (with respect to iron isotopic exchange) because they have fewer neighboring Fe octahedra and are therefore bound less strongly to the ferrihydrite structure. The labile population of sites probably is composed of end sites of the dioctahedral chain structure of 2-line ferrihydrite, which is a subset of the entire population of surface sites. Mössbauer spectra of samples containing adsorbed arsenate indicated that the anion may slightly decrease the distortion of labile sites and stabilized the structure as a whole by bidentate bonding.

Clays and Clay Minerals↗
USGS2018

Development of Raman spectroscopy as a thermal maturity proxy in unconventional resource assessment

The objective of this study was to correlate shale hydrous pyrolysis with thermal maturity measurements based on solid bitumen reflectance (BRo) at the U.S. Geological Survey (USGS) and Raman microscopy (RM) at WellDog. In semi-blind Phase I, BRo values of the initial set of 8 samples were withheld prior to RM analysis. As reported previously, a strong correlation was observed between BRo and Raman parameters. For Phase-II, BRo values for the second set of 8 samples were shared before RM. Observations from Phase-II are reported here as well as the ability of RM to correctly order the semi-blind Phase I samples. Immature shale samples from the Bakken (Phase-I) and Duvernay (Phase-II) formations were subjected to hydrous pyrolysis for 72 hours at temperatures from 280°C to 360°C. Rock residues from both series were mounted and polished (ASTM D2797) for analysis of BRo (ASTM D7708) and confocal laser-scanning Raman microscopy. For RM, multiple hyperspectral maps were collected from each sample, resulting in tens of thousands of spectra per sample. Map areas were ~5,000 μm2, with a spectrum collected from every square micrometer. The organic carbon G- (Graphitic-) and D- (Disordered) bands in each Raman spectrum were fit algorithmically to a multi-peak model, yielding a number of diagnostic parameters that correlate with changes occurring in samples as a result of thermal maturation and pyrolysis. Parameters extracted from analysis of Raman spectra were plotted against the previously determined BRo values to determine which Raman parameters best correlate with thermal maturity. Plotting two of the sample-averaged anonymized spectral parameters versus BRo in the Bakken series indicated an exponential trend with strong correlations (R2>0.8) as reported at URTeC in 2017 (MS-2671253). Similar strong relationships occurred in the Duvernay samples with respect to increasing maturity when using Partial Least-Squares analysis.

Conference Paper↗
USGS2014

Mapping advanced argillic alteration at Cuprite, Nevada, using imaging spectroscopy

Mineral maps based on Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data were used to study late Miocene advanced argillic alteration at Cuprite, Nevada. Distributions of Fe-bearing minerals, clays, micas, sulfates, and carbonates were mapped using the Tetracorder spectral-shape matching system. The Al content of white micas increases toward altered areas and near intrusive rocks. Alunite composition varies from pure K to intimate mixtures of Na-K endmembers with subpixel occurrences of huangite, the Ca analogue of alunite. Intimately mixed Na-K alunite marks areas of relatively lower alteration temperature, whereas co-occurring Na-alunite and dickite may delineate relict hydrothermal conduits. The presence of dickite, halloysite, and well-ordered kaolinite, but absence of disordered kaolinite, is consistent with acidic conditions during hydrothermal alteration. Partial lichen cover on opal spectrally mimics chalcedony, limiting its detection to lichen-free areas. Pods of buddingtonite are remnants of initial quartz-adularia-smectite alteration. Thus, spectral maps provide a synoptic view of the surface mineralogy, and define a previously unrecognized early steam-heated hydrothermal event. Faulting and episodes of hydrothermal alteration at Cuprite were intimately linked to upper plate movements above the Silver Peak-Lone Mountain detachment and growth, collapse, and resurgence of the nearby Stonewall Mountain volcanic complex between 8 and 5 Ma. Isotopic dating indicates that hydrothermal activity started at least by 7.61 Ma and ended by about 6.2 Ma. Spectral and stable isotope data suggest that Cuprite is a late Miocene low-sulfidation adularia-sericite type hot spring deposit overprinted by late-stage, steam-heated advanced argillic alteration formed along the margin of the Stonewall Mountain caldera.

Nevada↗
USGS2004

Preliminary report on using imaging spectroscopy to map ultramafic rocks, serpentinites, and tremolite-actinolite-bearing rocks in California

Airborne Visible/InfraRed Imaging Spectrometer (AVIRIS) data were collected in approximately 3- kilometer-wide swaths over selected areas in El Dorado and Plumas Counties that contain serpentinite and ultramafic rocks as part of an experiment to determine if potentially asbestos-bearing rocks could be identified spectrally. M ineral maps created from the AVIRIS data were used successfully to delineate exposures of serpentine and tremolite-actinolite/talc in areas with up to 70 percent vegetation cover in some cases. In other cases, the density of vegetation is so high that it prevented spectral identification by AVIRIS of minerals in those areas, thus there may be more serpentine and tremolite-actinolite/talc present than is shown on the mineral maps. It also is important to note that not all tremolite-actinolite is fibrous, and just because tremolite-actinolite was mapped, does not necessarily mean it is tremolite- or actinolite-asbestos. Finally, it is difficult to spectrally distinguish tremolite-actinolite from talc using AVIRIS. Serpentine has been detected outside of known serpentinite outcrop areas, mostly as aggregate that covers dirt roads. Four flight lines of AVIRIS data were analyzed over areas selected to show trends in degree of surface exposure as a function of elevation and vegetation cover. Field checking has verified the accuracy of the mineral maps at 25 accessible locations. Eleven additional flight lines remain to be analyzed and field checked pending future funding. AVIRIS mineral mapping has shown promise as a complement to field mapping but cannot replace it. Because AVIRIS is a remote-sensing technology, the presence of serpentine or tremolite-actinolite would have to be verified in the field by direct observation and by appropriate sampling and laboratory analysis, if needed. At this time, no conclusions regarding the presence or absence of asbestos minerals in the identified areas are possible from the AVIRIS data alone. Identification of asbestos minerals in the identified areas would require appropriate sampling and laboratory analysis of the materials in those areas.

California↗
USGS2005

Remote sensing characterization of the Animas River watershed, southwestern Colorado, by AVIRIS imaging spectroscopy

Visible-wavelength and near-infrared image cubes of the Animas River watershed in southwestern Colorado have been acquired by the Jet Propulsion Laboratory's Airborne Visible and InfraRed Imaging Spectrometer (AVIRIS) instrument and processed using the U.S. Geological Survey Tetracorder v3.6a2 implementation. The Tetracorder expert system utilizes a spectral reference library containing more than 400 laboratory and field spectra of end-member minerals, mineral mixtures, vegetation, manmade materials, atmospheric gases, and additional substances to generate maps of mineralogy, vegetation, snow, and other material distributions. Major iron-bearing, clay, mica, carbonate, sulfate, and other minerals were identified, among which are several minerals associated with acid rock drainage, including pyrite, jarosite, alunite, and goethite. Distributions of minerals such as calcite and chlorite indicate a relationship between acid-neutralizing assemblages and stream geochemistry within the watershed. Images denoting material distributions throughout the watershed have been orthorectified against digital terrain models to produce georeferenced image files suitable for inclusion in Geographic Information System databases. Results of this study are of use to land managers, stakeholders, and researchers interested in understanding a number of characteristics of the Animas River watershed.

Scientific Investigations Report↗
USGS2013

Iron mineralogy and bioaccessibility of dust generated from soils as determined by reflectance spectroscopy and magnetic and chemical properties--Nellis Dunes recreational area, Nevada

Atmospheric mineral dust exerts many important effects on the Earth system, such as atmospheric temperatures, marine productivity, and melting of snow and ice. Mineral dust also can have detrimental effects on human health through respiration of very small particles and the leaching of metals in various organs. These effects can be better understood through characterization of the physical and chemical properties of dust, including certain iron oxide minerals, for their extraordinary radiative properties and possible effects on lung inflammation. Studies of dust from the Nellis Dunes recreation area near Las Vegas, Nevada, focus on characteristics of radiative properties (capacity of dust to absorb solar radiation), iron oxide mineral type and size, chemistry, and bioaccessibility of metals in fluids that simulate human gastric, lung, and phagolysosomal fluids. In samples of dust from the Nellis Dunes recreation area with median grain sizes of 2.4, 3.1, and 4.3 micrometers, the ferric oxide minerals goethite and hematite, at least some of it nanosized, were identified. In one sample, in vitro bioaccessibility experiments revealed high bioaccessibility of arsenic in all three biofluids and higher leachate concentration and bioaccessibility for copper, uranium, and vanadium in the simulated lung fluid than in the phagolysosomal fluid. The combination of methods used here to characterize mineral dust at the Nellis Dunes recreation area can be applied to global dust and broad issues of public health.

Nevada↗
USGS1971

Determination of minor elements in water by emission spectroscopy

With the emission spectrograph, the analyst is able to determine many minor elements simultaneously in water samples. Spectrographic methods differ chiefly in techniques of preconcentrating the elements. For waters with dissolved solids of less than 1,000 milligrams per liter, the method of evaporating to dryness and determining the elements in the dried residue is sensitive, precise, and reasonably accurate. The lower limits of detection vary with the quantity of dissolved solids. Twenty-four elements are determined by this method. For waters with more than 1,000 milligrams per liter of dissolved solids, it is necessary to separate the minor elements from the major constituents before spectrographically determining the former, in order to achieve adequate lower limits of detection. Such procedures generally require more time than the residue method. In the first of two such procedures given, 21 of the metallic elements are precipitated with thioacetamide prior to spectrographic determination. In an alternate procedure, 18 elements are precipitated quantitatively with complexing reagents 8-hydroxyquinoline, tannic acid, and thioanlide. This method is faster than the thioacetamide method, but at the sacrifice of some elements. A Fortran IV computer program for processing densitometric data is given in the section 'Computer Program.'

Techniques of Water-Resources Investigations↗
USGS1997

The forms of trace metals in an Illinois basin coal by x-ray absorption fine structure spectroscopy

Utilities burning Illinois coals currently do not consider trace elements in their flue gas emissions. After the US EPA completes an investigation on trace elements, however, this may change and flue gas emission standards may be established. The mode of occurrence of a trace element may determine its cleanability and Hue gas emission potential. X-ray Absorption Fine Structure (XAFS) is a spectroscopic technique that can differentiate the mode of occurrence of an element, even at the low concentrations that trace elements are found in coal. This is principally accomplished by comparing the XAFS spectra of a coal to a database of reference sample spectra. This study evaluated the technique as a potential tool to examine six trace elements in an Illinois #6 coal. For the elements As and Zn, the present database provides a definitive interpretation on their mode of occurrence. For the elements Ti, V, Cr, and Mn the database of XAFS spectra of trace elements in coal was still too limited to allow a definitive interpretation. The data obtained on these elements, however, was sufficient to rule out several of the mineralogical possibilities that have been suggested previously. The results indicate that XAFS is a promising technique for the study of trace elements in coal.

ACS Division of Fuel Chemistry, Preprints↗
USGS1973

Fluorescent spectroscopy, a technique for characterizing surface films

A relationship is established between fluorescent spectra obtained by using a light path through the liquid solution and the fluorescent spectra obtained by a direct reading of surface reflection (remote sensing). A brief review of quantum fundamentals provides the necessary information to conclude that "see-through" and reflectance spectra are identical in wavelength response. Many floating films contain fluorescent materials; thus fluorescent spectroscopic techniques were used to obtain the fluorescent spectra of lube oil, crude oil, and lignosulfonie acid in an effort to detect, identify, and quantify these representative fluorescent materials in water solutions. For each material tested the emission maximum was established. The emission maximum was then held constant while the absorption spectrum was recorded and the absorption maximum established. The complete spectral curves are presented.

Journal of Research of the U.S. Geological Survey↗