scholarly journals Grain-Scale Analysis of Solid-Phase Organic Matter and Arsenic Mobility in Mining-Impacted 1 Sediment from Sub‐Arctic Lakes, Northwest Territories, Canada

2021 ◽  
Author(s):  
Clare B Miller ◽  
Michael B Parsons ◽  
Heather E Jamieson ◽  
Omid H Ardakani ◽  
R Timothy Patterson ◽  
...  
Keyword(s):  
Organic Matter ◽  
Northwest Territories ◽  
Solid Phase ◽  
Arctic Lakes ◽  
Edge Structure ◽  
Near Surface ◽  
X Ray ◽  
Fine Grained ◽  
Arsenic Mobility ◽  
Co Precipitation

Abstract Arsenic (As) is commonly sequestered at the sediment-water interface (SWI) in mining-impacted lakes through adsorption and/or co-precipitation with authigenic iron (Fe)-(oxy)hydroxides or sulphides. The results of this study demonstrate that the accumulation of solid-phase organic matter (OM) in near-surface sediments also influences the mobility and fate of As in sub-Arctic lakes. Sediment gravity cores, sediment grab samples, and porewaters were collected from three lakes downstream of the former Tundra gold mine, Northwest Territories. Analysis of sediment using combined micro-X-ray fluorescence/diffraction, K-edge X-ray Absorption Near-Edge Structure (XANES), and organic petrography shows that As is associated with both aquatic (benthic and planktonic alginate) and terrestrially-derived OM (cutinite; funginite). Most As is hosted by fine-grained Fe-(oxy)hydroxides or sulphide minerals ( e.g., goethite, orpiment, lepidocrocite, mackinawite); however, grain-scale synchrotron-based analysis shows that As is also associated with amorphous OM. Mixed As oxidation states in porewater (median = 62 % As (V), 18 % As (III); n = 20) and sediment (median = 80 % As (-I) and (III), 19 % As (V); n = 9) indicate the presence of variable redox conditions in the near-surface sediment and suggest that post-depositional remobilization of As has occurred . Detailed characterization of As-bearing OM at and below the SWI suggests that OM plays an important role in stabilizing redox-sensitive authigenic minerals and associated As. Based on these findings, it is expected that increased concentrations of labile OM will drive post-depositional surface-enrichment of As in mining-impacted lakes and may increase or decrease As flux from sediments to overlying surface waters.

scholarly journals Neptunium Reactivity During Co-Precipitation and Oxidation of Fe(II)/Fe(III) (Oxyhydr)oxides

Geosciences ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 27 ◽  
Author(s):  
Hannah E. Roberts ◽  
Katherine Morris ◽  
J. Frederick W. Mosselmans ◽  
Gareth T. W. Law ◽  
Samuel Shaw
Keyword(s):  
Green Rust ◽  
Solution Chemistry ◽  
Natural Environments ◽  
Edge Structure ◽  
X Ray ◽  
End Point ◽  
Mineral Phases ◽  
Oxidation In Air ◽  
Co Precipitation ◽  
X Ray Absorption

Fe(II) bearing iron (oxyhydr)oxides were directly co-precipitated with Np(V)O2+ under anaerobic conditions to form Np doped magnetite and green rust. These environmentally relevant mineral phases were then characterised using geochemical and spectroscopic analyses. The Np doped mineral phases were then oxidised in air over 224 days with solution chemistry and end-point oxidation solid samples collected for further characterisation. Analysis using chemical extractions and X-ray absorption spectroscopy (XAS) techniques confirmed that Np(V) was initially reduced to Np(IV) during co-precipitation of both magnetite and green rust. Extended X-Ray Absorption Fine Structure (EXAFS) modelling suggested the Np(IV) formed a bidentate binuclear sorption complex to both minerals. Furthermore, following oxidation in air over several months, the sorbed Np(IV) was partially oxidised to Np(V), but very little remobilisation to solution occurred during oxidation. Here, linear combination fitting of the X-Ray Absorption Near Edge Structure (XANES) for the end-point oxidation samples for both mineral phases suggested approximately 50% oxidation to Np(V) had occurred over 7 months of oxidation in air. Both the reduction of Np(V) to Np(IV) and inner sphere sorption in association with iron (oxyhydr)oxides, and the strong retention of Np(IV) and Np(V) species with these phases under robust oxidation conditions, have important implications in understanding the mobility of neptunium in a range of engineered and natural environments.

scholarly journals Three dimensional soil organic matter distribution, accessibility and microbial respiration in macro-aggregates using osmium staining and synchrotron X-ray CT

2016 ◽  
Author(s):  
Barry G Rawlins ◽  
Joanna Wragg ◽  
Christina Rheinhard ◽  
Robert C Atwood ◽  
Alasdair Houston ◽  
...  
Keyword(s):  
Organic Matter ◽  
Transition Probabilities ◽  
Solid Phase ◽  
Pore Space ◽  
Three Dimensional ◽  
Soil Core ◽  
Length Scales ◽  
X Ray ◽  
Mineral Phases ◽  
Indicator Variograms

Abstract. The spatial distribution and accessibility of organic matter (OM) to soil microbes in aggregates – determined by the fine-scale, 3-D distribution of organic matter, pores and mineral phases – may be an important control on the magnitude of soil heterotrophic respiration (SHR). Attempts to model SHR at fine scales requires data on the transition probabilities between adjacent pore space and soil OM, a measure of microbial accessibility to the latter. We used a combination of osmium staining and synchrotron X-ray CT to determine the 3-D (voxel) distribution of these three phases (scale 6.6 μm) throughout nine aggregates taken from a single soil core (range of organic carbon (OC) concentrations 4.2–7.7 %). Prior to the synchrotron analyses we had measured the magnitude of SHR for each aggregate over 24 hours under controlled conditions (moisture content and temperature). We test the hypothesis that larger magnitudes of SHR will be observed in aggregates with shorter length scales of OM variation (i.e. more frequent, and possibly more finely disseminated, OM and a larger number of aerobic microsites). After scaling to their OC concentrations, there was a six-fold variation in the magnitude of SHR for the nine aggregates. The distribution of pore volumes, pore shape and volume normalised surface area were similar for each of the nine aggregates. The overall transition probabilities between OM and pore voxels were between 0.02 and 0.03, significantly smaller than those used in previous simulation studies. We computed the length scales over which OM, pore and mineral phases vary within each aggregate using indicator variograms. The median range of models fitted to variograms of OM varied between 178 and 487 μm. The linear correlation between these median length scales of OM variation and the magnitudes of SHR for each aggregate was −0.42, providing some evidence to support our hypothesis. We require a larger number of observations to make a statistical inference. There was no evidence to suggest a statistical relationship between OM:pore transition probabilities and the magnitudes of aggregate SHR. The solid-phase volume proportions (45–63 %) of OM we report for our aggregates were surprisingly large by comparison to those assumed in previous modelling approaches. We suggest this requires further assessment using accurate measurements of OM bulk density in a range of soil types.

Co-Promoted Cu/ZnO Catalysts for Fischer-Tropsch Synthesis

2017 ◽  
Vol 266 ◽  
pp. 117-121
Author(s):  
Piyasak Akcaboot ◽  
Napat Kanokpornwasin ◽  
Monthida Raoarun ◽  
Patraporn Saiwattanasuk ◽  
Pinsuda Viravathana
Keyword(s):  
Tropsch Synthesis ◽  
Precipitation Method ◽  
X Ray Diffraction ◽  
Fischer Tropsch ◽  
Edge Structure ◽  
Fischer Tropsch Synthesis ◽  
X Ray ◽  
Cu Foil ◽  
Co Precipitation ◽  
X Ray Absorption

Co-promoted Cu/ZnO catalysts were studied for Fischer-Tropsch synthesis (FTS). All catalysts were prepared by the co-precipitation method, having the mass ratio of Co:Cu:Zn=0 (unpromoted), 0.05, 0.5:1:1, and characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). From XRD and XAS, the results confirmed the phase transformation of CuO to Cu foil and Co3O4 to Co foil in Co-promoted catalysts after reduction. After FTS reaction testing, the Co-promoted catalysts showed the decrease in methanol selectivity of 15 and 1.6% for 0.05Co-Cu/ZnO and 0.5Co-Cu/ZnO, respectively, and the increase in C5-C15 selectivity during 30 h of reaction.

Investigation of Organic Matter Entrapped in Synthetic Carbonates—A Multimethod Approach

2012 ◽  
Vol 19 (1) ◽  
pp. 132-144 ◽  
Author(s):  
Emilie Chalmin ◽  
Yves Perrette ◽  
Bernard Fanget ◽  
Jean Susini
Keyword(s):  
Organic Matter ◽  
Fourier Transform ◽  
Infrared Spectroscopy ◽  
Edge Structure ◽  
X Ray ◽  
Multimethod Approach ◽  
The Stability ◽  
Log Linear ◽  
X Ray Absorption ◽  
Surface Changes

AbstractOrganic matter (OM) entrapped in calcite is regularly used for environmental studies; however, insertion mechanisms and types of interaction remain poorly understood. The present study used a new methodology to investigate interactions between OM and the calcite matrix during crystallization processes with humic acid (HA) entrapment. A multimethod approach confirmed that HA is both adsorbed onto the calcite surface and incorporated into the calcite lattice during crystallization. Our results also confirm the log-linear correlation between fluorescence intensity and calcite matrix HA concentration. Fourier transform infrared spectroscopy showed that HA in colloidal conformation is adsorbed onto the calcite surface as a result of the structure of the OH stretching band. We also developed a new method based on synchrotron analysis that uses sulfur as a tracer element for entrapped HA and that localizes the OM electrostatically adsorbed onto the calcite surface. Changes in the sulfur environment, determined using X-ray absorption near-edge structure spectroscopy, indicated more complex insertion mechanisms than simple adsorption of HA during calcite crystallization. Desorption experiments revealed the stability of the OM atomic structure and its layered nature. These results allowed us to draw up a general model of OM insertion in calcite.

scholarly journals The Origin of Organic Matter in the Solar System: Evidence from the Interplanetary Dust Particles

2004 ◽  
Vol 213 ◽  
pp. 275-280 ◽  
Author(s):  
G. J. Flynn ◽  
L. P. Keller ◽  
C. Jacobsen ◽  
S. Wirick
Keyword(s):  
Organic Matter ◽  
Gas Phase ◽  
Interplanetary Dust ◽  
Dust Particles ◽  
Aqueous Processing ◽  
Interplanetary Dust Particles ◽  
Volatile Elements ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

Interplanetary dust particles (IDPs), ∼ 10μm particles from comets and asteroids, have been collected by NASA from the Earth's stratosphere. We compared carbon X-ray Absorption Near-Edge Structure (XANES) and Fourier Transform Infra-Red (FTIR) spectra of anhydrous and hydrated interplanetary dust particles and found that anhydrous and hydrated IDPs have similar types and abundances of organic carbon. This is different from results on meteorites, which show that hydrated carbonaceous meteorites contain abundant organic matter, while anhydrous carbonaceous meteorites contain less carbon mostly in elemental form. But all anhydrous carbonaceous meteorites are depleted in moderately volatile and volatile elements in a pattern that suggested they experienced temperatures in excess of 1200°C, a temperature sufficient to destroy any organic matter they originally contained, while many anhydrous IDPs show no evidence of severe heating. These IDP results indicate that the bulk of the pre-biotic organic matter in extraterrestrial materials formed before aqueous processing, possibly by irradiation of C-bearing ices or by a Fisher-Tropsch type process operating in the gas phase of the nebula or in the interstellar medium.

Titanium coordination in silicate glasses investigated using O K-edge X-ray absorption spectroscopy

2003 ◽  
Vol 67 (4) ◽  
pp. 597-607 ◽  
Author(s):  
G. S. Henderson ◽  
Xiaoyang Liu ◽  
M. E. Fleet
Keyword(s):  
Glass Sample ◽  
Surface Region ◽  
Bulk Sample ◽  
Silicate Glasses ◽  
Titanium Silicate ◽  
Edge Structure ◽  
Near Surface ◽  
X Ray ◽  
Edge Features ◽  
X Ray Absorption

AbstractA series of titanium silicate glasses along the composition joins TiO2-SiO2, TiO2-Na2SiO3, TiO2-K2SiO3 and TiO2-CaSiO3, has been examined using oxygen K-edge X-ray absorption near edge structure spectroscopy (XANES) confined to the near-surface region. Sharp pre-edge features in the spectra can be used to determine the Ti coordination in the glasses. The presence of [4]Ti is indicated by a pre-edge peak at ∼534 eV while [5]Ti is indicated by a peak at ∼533 eV. Titanium exists in all these glasses as [4]Ti and [5]Ti with no [6]Ti being present. For alkali-containing glasses the [5]Ti site becomes more prevalent with increasing TiO2. TiO2-K2SiO3 compositions contain a greater proportion of [4]Ti than comparable Na2O compositions. This is consistent with earlier Ti L-edge findings. The TEY spectra for the TiO2-CaSiO3 compositions indicate the presence of significant amounts of [5]Ti at high TiO2 contents; however, comparison of TEY (near surface) and FY (bulk sample) XANES shows that the [5]Ti is confined to the surface of the glass sample with the bulk of the glass containing [4]Ti.

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