scholarly journals Geochemical Controls on Release and Speciation of Fe(II) and Mn(II) From Hyporheic Sediments of East River, Colorado

2020 ◽  
Vol 2 ◽  
Author(s):  
Wenming Dong ◽  
Amrita Bhattacharyya ◽  
Patricia M. Fox ◽  
Markus Bill ◽  
Dipankar Dwivedi ◽  
...  
Keyword(s):  
Hyporheic Zone ◽  
Solid Phase ◽  
Equilibrium Concentration ◽  
Binding Constants ◽  
East River ◽  
Reducing Conditions ◽  
Incubation Experiments ◽  
Subsurface Environments ◽  
Hyporheic Zones ◽  
Geochemical Controls

Hyporheic zones act as critical ecological links between terrestrial and aquatic systems where redox-sensitive metals of iron (Fe) and manganese (Mn) significantly impact nutrient cycling and water quality. However, the geochemical controls on the release and speciation of Fe(II) and Mn(II) in these biogeochemical hotspots are still poorly understood. Here we conducted batch incubation experiments and analyzed Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy data using sediment samples from a hyporheic zone of the East River floodplain in Colorado to understand the production, release and speciation of Fe(II) and Mn(II) in groundwater. Our results indicate that the production and release of Fe(II) and Mn(II) vary with sediment reducing conditions and subsurface positions, and the rates were determined either by a zero- or first-order rate equation. The sediments with higher Fe(II) production did not necessarily result in higher release of dissolved Fe(II), and ≥97% Fe(II) is accumulated in solid phase. We found that the majority of Fe(II) exists as siderite (FeCO3), Fe(II)-natural organic matter (NOM) complexes and ferrosmectite, and the equilibrium concentrations of dissolved Fe(II) are controlled primarily by siderite solubility, and enhanced greatly by formation of strong Fe(II)-NOM complexes as dominant aqueous Fe(II) species. By contract, dissolved Mn(II) increases slowly and linearly, and an equilibrium concentration was not reached during the incubation period, and the roles of rhodochrosite (MnCO3) and Mn(II)-NOM complexes are insignificant. Furthermore, we reviewed and calibrated the literature reported binding constants (log K) of Fe(II)-NOM complexes which successfully predicted our experimental data. This work reveals that siderite and dissolved NOM are the controlling phases in release and speciation of dissolved Fe(II), and the finding is expected to be applicable in many hyporheic zones and subsurface environments with similar geochemical conditions.

Iodine Release from Silver Iodide under Reducing Condition with Iron-Bearing Minerals

2002 ◽  
Vol 713 ◽  
Author(s):  
X. Xia ◽  
Y. Inagaki ◽  
A. Hattori ◽  
K. Idemitsu ◽  
T. Arima
Keyword(s):  
Silver Iodide ◽  
Solid Phase ◽  
Equilibrium Concentration ◽  
Metallic Silver ◽  
Reducing Conditions ◽  
Key Factor ◽  
Solution Kinetic ◽  
Iodine Release ◽  
Iron Bearing ◽  
Reducing Condition

ABSTRACTIodine release from silver iodide (AgI) to water was evaluated under reducing conditions in the presence of iron-bearing minerals, goethite (FeOOH), magnetite (Fe3O4) and Wüstite (FeO). The release tests were performed in a glove box purged with gas mixture (Ar+5%H2), and the concentrations of dissolved iodine, silver and iron were measured. The apparent equilibrium concentration of dissolved iodine was 4.0 ×10−8, 4.3×10−8 mol/l for the tests with FeOOH and Fe3O4, respectively. The values were almost the same as in the test without minerals. For the test with FeO, the concentration of dissolved iodine was 5.4×10−3 mol/l, which is five orders of magnitude higher than for the other tests. Solid phase analyses by using XRD and SEM/EDS indicated that metallic silver precipitated on the surface of the original AgI for the test with FeO and on the surface of Fe3O4 for the test with Fe3O4, but not for that with FeOOH. These results showed that only FeO could reduce AgI effectively to increase iodine release. The amount of dissolved Fe(II) was a key factor affecting AgI reduction instead of redox potential of solution. Kinetic processes may also play an important role in AgI reduction and associated iodine release under reducing condition.

scholarly journals Hidden Processes During Seasonal Isolation of a High-Altitude Watershed

2021 ◽  
Vol 9 ◽  
Author(s):  
Jessica Z. Buser-Young ◽  
Laura L. Lapham ◽  
Andrew R. Thurber ◽  
Kenneth H. Williams ◽  
Frederick S. Colwell
Keyword(s):  
Surface Water ◽  
High Altitude ◽  
Hyporheic Zone ◽  
Taxonomic Composition ◽  
Early Summer ◽  
Methane Cycling ◽  
East River ◽  
Hyporheic Zones ◽  
O Isotopes ◽  
Global Carbon

Biogeochemical processes capable of altering global carbon systems occur frequently in Earth’s Critical Zone–the area spanning from vegetation canopy to saturated bedrock–yet many of these phenomena are difficult to detect. Observation of these processes is limited by the seasonal inaccessibility of remote ecosystems, such as those in mountainous, snow- and ice-dominated areas. This isolation leads to a distinct gap in biogeochemical knowledge that ultimately affects the accuracy and confidence with which these ecosystems can be computationally modeled for the purpose of projecting change under different climate scenarios. To examine a high-altitude, headwater ecosystem’s role in methanogenesis, sulfate reduction, and groundwater-surface water exchange, water samples were continuously collected from the river and hyporheic zones (HZ) during winter isolation in the East River (ER), CO watershed. Measurements of continuously collected ER surface water revealed up to 50 μM levels of dissolved methane in July through September, while samples from 12 cm deep in the hyporheic zone at the same location showed a spring to early summer peak in methane with a strong biogenic signature (<65 μM, δ13C-CH4, −60.76‰) before declining. Continuously collected δ18O-H2O and δ2H-H2O isotopes from the water column exhibited similar patterns to discrete measurements, while samples 12 cm deep in the hyporheic zone experienced distinct fluctuations in δ18O-H2O, alluding to significant groundwater interactions. Continuously collected microbial communities in the river in the late fall and early winter revealed diverse populations that reflect the taxonomic composition of ecologically similar river systems, including taxa indicative of methane cycling in this system. These measurements captured several biogeochemical components of the high-altitude watershed in response to seasonality, strengthening our understanding of these systems during the winter months.

Effects of riffle–step restoration on hyporheic zone chemistry in N-rich lowland streams

2006 ◽  
Vol 63 (1) ◽  
pp. 120-133 ◽  
Author(s):  
Tamao Kasahara ◽  
Alan R Hill
Keyword(s):  
Urban Areas ◽  
Hyporheic Zone ◽  
Stream Water ◽  
Ion Concentration ◽  
Hyporheic Exchange ◽  
Ecosystem Functions ◽  
Exchange Flow ◽  
Nutrient Inputs ◽  
Lowland Streams ◽  
Hyporheic Zones

Stream restoration projects that aim to rehabilitate ecosystem health have not considered surface–subsurface linkages, although stream water and groundwater interaction has an important role in sustaining stream ecosystem functions. The present study examined the effect of constructed riffles and a step on hyporheic exchange flow and chemistry in restored reaches of several N-rich agricultural and urban streams in southern Ontario. Hydrometric data collected from a network of piezometers and conservative tracer releases indicated that the constructed riffles and steps were effective in inducing hyporheic exchange. However, despite the use of cobbles and boulders in the riffle construction, high stream dissolved oxygen (DO) concentrations were depleted rapidly with depth into the hyporheic zones. Differences between observed and predicted nitrate concentrations based on conservative ion concentration patterns indicated that these hyporheic zones were also nitrate sinks. Zones of low hydraulic conductivity and the occurrence of interstitial fines in the restored cobble-boulder layers suggest that siltation and clogging of the streambed may reduce the downwelling of oxygen- and nitrate-rich stream water. Increases in streambed DO levels and enhancement of habitat for hyporheic fauna that result from riffle–step construction projects may only be temporary in streams that receive increased sediment and nutrient inputs from urban areas and croplands.

Impact of sulfate on the solubility of Tc(IV) in acidic to hyperalkaline aqueous reducing systems

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Sarah B. Duckworth ◽  
Xavier Gaona ◽  
Alexander Baumann ◽  
Kathy Dardenne ◽  
Jörg Rothe ◽  
...  
Keyword(s):  
Solid Phase ◽  
Correction Factors ◽  
Mixed Salt ◽  
Ph Values ◽  
Reducing Conditions ◽  
Upper Limits ◽  
Salt Systems ◽  
Amorphous Character ◽  
Good Agreement

Abstract The solubility of 99Tc(IV) was investigated from undersaturation conditions in NaCl–Na2SO4 (0.3 M ≤ I ≤ 5.0 M), MgCl2–MgSO4 (I = 13.5 M) and CaCl2–CaSO4 (I = 13.5 M) systems with 0.001 M ≤ [SO4 2−]tot ≤ 1.0 M and 1 ≤ pH m  ≤ 12 (with pH m  = −log[H+], in molal units). Reducing conditions were set by either Sn(II) or Fe(0). Special efforts were dedicated to accurately characterize the correction factors A m required for the determination of pH m from the experimentally measured pH values in the mixed salt systems investigated, with pH m  = pHexp + A m . The combination of (pe + pH m ) measurements with Pourbaix diagrams of Tc suggests that technetium is present in its +IV redox state. This hypothesis is confirmed by XANES, which unambiguously shows the predominance of Tc(IV) both in the aqueous and solid phases of selected solubility samples. XRD and SEM–EDS support the amorphous character of the solid phase controlling the solubility of Tc(IV). EXAFS data confirm the predominance of TcO2(am, hyd) at pH m  > 1.5, whereas the formation of a Tc(IV)–O–Cl solid phase is hinted at lower pHm values in concentrated NaCl–Na2SO4 systems with ≈5 M NaCl. Solubility data collected in sulfate-containing systems are generally in good agreement with previous solubility studies conducted in sulfate-free NaCl, MgCl2 and CaCl2 solutions of analogous ionic strength. Although the complexation of Tc(IV) with sulfate cannot be completely ruled out, these results strongly support that, if occurring, complexation must be weak and has no significant impact on the solubility of Tc(IV) in dilute up to highly saline media. Solubility upper-limits determined in this work can be used for source term estimations including the effect of sulfate in a variety of geochemical conditions relevant in the context of nuclear waste disposal.

A numerical study of the nucleation, growth and settling of crystals from a turbulent convecting fluid

2021 ◽  
Author(s):  
Vojtech Patocka ◽  
Nicola Tosi ◽  
Enrico Calzavarini
Keyword(s):  
Magma Chamber ◽  
Solid Fraction ◽  
Large Scale ◽  
Solid Phase ◽  
Numerical Study ◽  
Equilibrium Concentration ◽  
Solid Particles ◽  
Settling Rate ◽  
Carrier Fluid ◽  
Nucleation Growth

<p>We evaluate the equilibrium concentration of a thermally convecting suspension that is cooled from above and in which<br>solid crystals are self-consistently generated in the thermal boundary layer near the top. In a previous study (Patočka et<br>al., 2020), we investigated the settling rate of solid particles suspended in a highly vigorous (Ra = 10<sup>8</sup> , 10<sup>10</sup>, and 10<sup>12</sup> ),<br>finite Prandtl number (Pr = 10, 50) convection. In this follow-up study we additionally employ the model of crystal<br>generation and growth of Jarvis and Woods (1994), instead of using particles with a predefined size and density that are<br>uniformly injected into the carrier fluid.</p><p>We perform a series of numerical experiments of particle-laden thermal convection in 2D and 3D Cartesian geometry<br>using the freely available code CH4 (Calzavarini, 2019). Starting from a purely liquid phase, the solid fraction gradually<br>grows until an equilibrium is reached in which the generation of the solid phase balances the loss of crystals due to<br>sedimentation at the bottom of the fluid. For a range of predefined density contrasts of the solid phase with respect to<br>the density of the fluid (ρ<sub>p</sub> /ρ<sub>f</sub> = [0, 2]), we measure the time it takes to reach such equilibrium. Both this time and<br>the equilibrium concentration depend on the average settling rate of the particles and are thus non-trival to compute for<br>particle types that interact with the large-scale circulation of the fluid (see Patočka et al., 2020).</p><p>We apply our results to the cooling of a large volume of magma, spanning from a large magma chamber up to a<br>global magma ocean. Preliminary results indicate that, as long as particle re-entrainment is not a dominant process, the<br>separation of crystals from the fluid is an efficient process. Fractional crystallization is thus expected and the suspended<br>solid fraction is typically small, prohibiting phenomena in which the feedback of crystals on the fluid begins to govern the<br>physics of the system (e.g. Sparks et al, 1993).</p><p>References<br>Patočka V., Calzavarini E., and Tosi N.(2020). Settling of inertial particles in turbulent Rayleigh-Bénard convection.<br>Physical Review Fluids, 26(4) 883-889.</p><p>Jarvis, R. A. and Woods, A. W.(1994). The nucleation, growth and settling of crystals from a turbulently convecting<br>fluid. J. Fluid. Mech, 273 83-107.</p><p>Sparks, R., Huppert, H., Koyaguchi, T. et al (1993). Origin of modal and rhythmic igneous layering by sedimentation in<br>a convecting magma chamber. Nature, 361, 246-249.</p><p>Calzavarini, E (2019). Eulerian–Lagrangian fluid dynamics platform: The ch4-project. Software Impacts, 1, 100002.</p>

scholarly journals Tunable Mn Oxidation State and Redox Potential of Birnessite Coexisting with Aqueous Mn(II) in Mildly Acidic Environments

Minerals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 690
Author(s):  
Juan Liu ◽  
Yixiao Zhang ◽  
Qian Gu ◽  
Anxu Sheng ◽  
Baogang Zhang
Keyword(s):  
Oxidation State ◽  
Organic Pollutant ◽  
Equilibrium Concentration ◽  
Aquatic Environments ◽  
Oxidation Potentials ◽  
Average Oxidation State ◽  
Subsurface Environments ◽  
Equilibrium Concentrations ◽  
Kinetics Of ◽  
Manganese Oxide Mineral

As the dominant manganese oxide mineral phase in terrestrial and aquatic environments, birnessite plays an important role in many biogeochemical processes. The coexistence of birnessite with aqueous Mn2+ is commonly found in the subsurface environments undergoing Mn redox cycling. This study investigates the change in Mn average oxidation state (AOS) of birnessite after reaction with 0.1–0.4 mM Mn2+ at pH 4.5–6.5, under conditions in which phase transformation of birnessite by Mn2+ was not detectable. The amount of Mn2+ uptake by birnessite and the equilibrium concentration of Mn(III) proportionally increased with the initial concentration of Mn2+. The Mn AOS of birnessite particles became 3.87, 3.75, 3.64, and 3.53, respectively, after reaction with 0.1, 0.2, 0.3, and 0.4 mM Mn2+ at pH 5.5. Oxidation potentials (Eh) of birnessite with different AOS values were estimated using the equilibrium concentrations of hydroquinone oxidized by the birnessite samples, indicating that Eh was linearly proportional to AOS. The oxidation kinetics of bisphenol A (BPA), a model organic pollutant, by birnessite suggest that the logarithms of surface area-normalized pseudo-first-order initial rate constants (log kSA) for BPA degradation by birnessite were linearly correlated with the Eh or AOS values of birnessite with AOS greater than 3.64.

Assessment of Redox Conditions in the Near Field of Nuclear Waste Repositories: Application to the Swiss high-level and intermediate level waste disposal concept

2003 ◽  
Vol 807 ◽  
Author(s):  
Paul Wersin ◽  
Lawrence H. Johnson ◽  
Bernhard Schwyn
Keyword(s):  
Solid Phase ◽  
Near Field ◽  
Intermediate Level ◽  
Redox Conditions ◽  
High Level Waste ◽  
Redox Potentials ◽  
Spent Fuel ◽  
Reducing Conditions ◽  
High Level ◽  
Waste Repositories

ABSTRACTRedox conditions were assessed for a spent fuel and high-level waste (SF/HLW) and an intermediate-level waste (ILW) repository. For both cases our analysis indicates permanently reducing conditions after a relatively short oxic period. The canister-bentonite near field in the HLW case displays a high redox buffering capacity because of expected high activity of dissolved and surface-bound Fe(II). This is contrary to the cementitious near field in the ILW case where concentrations of dissolved reduced species are low and redox reactions occur primarily via solid phase transformation processes.For the bentonite-canister near field, redox potentials of about -100 to -300 mV (SHE) are estimated, which is supported by recent kinetic data on U, Tc and Se interaction with reduced iron systems. For the cementitious near field, redox potentials of about -200 to -800 mV are estimated, which reflects the large uncertainties related to this alkaline environment.

scholarly journals Impact of Bed Form Celerity on Oxygen Dynamics in the Hyporheic Zone

Water ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 62 ◽  
Author(s):  
Philipp Wolke ◽  
Yoni Teitelbaum ◽  
Chao Deng ◽  
Jörg Lewandowski ◽  
Shai Arnon
Keyword(s):  
Hyporheic Zone ◽  
Time Lapse ◽  
Oxygen Distribution ◽  
Anoxic Zone ◽  
Fine Grain ◽  
Uptake Rates ◽  
Hyporheic Zones ◽  
Bed Form ◽  
Gradual Disappearance ◽  
Oxygen Dynamics

Oxygen distribution and uptake in the hyporheic zone regulate various redox-sensitive reactions and influence habitat conditions. Despite the fact that fine-grain sediments in streams and rivers are commonly in motion, most studies on biogeochemistry have focused on stagnant sediments. In order to evaluate the effect of bed form celerity on oxygen dynamics and uptake in sandy beds, we conducted experiments in a recirculating indoor flume. Oxygen distribution in the bed was measured under various celerities using 2D planar optodes. Bed morphodynamics were measured by a surface elevation sensor and time-lapse photography. Oxygenated zones in stationary beds had a conchoidal shape due to influx through the stoss side of the bed form, and upwelling anoxic water at the lee side. Increasing bed celerity resulted in the gradual disappearance of the upwelling anoxic zone and flattening of the interface between the oxic (moving fraction of the bed) and the anoxic zone (stationary fraction of the bed), as well as in a reduction of the volumetric oxygen uptake rates due shortened residence times in the hyporheic zone. These results suggest that including processes related to bed form migration are important for understanding the biogeochemistry of hyporheic zones.

Aqueous Dissolution of Silver Iodide and Associated Iodine Release under Reducing Conditions with Sulfide

2006 ◽  
Vol 985 ◽  
Author(s):  
Yaohiro Inagaki ◽  
Toshitaka Imamura ◽  
Kazuya Idemitsu ◽  
Tatsumi Arima ◽  
Osamu Kato ◽  
...  
Keyword(s):  
Thin Layer ◽  
Phase Analysis ◽  
Thermodynamic Equilibrium ◽  
Silver Iodide ◽  
Solid Phase ◽  
Reducing Conditions ◽  
Dissolution Tests ◽  
Iodine Release

AbstractAqueous dissolution tests of AgI were performed in Na2S solutions in order to evaluate, empirically, dissolution of AgI to release iodine under reducing conditions with sulfide. The results indicated that AgI dissolves to release iodine being controlled by mainly precipitation of Ag2S. However, the dissolution of AgI can be depressed to proceed, and the thermodynamic equilibrium cannot be attained easily. Solid phase analysis for the reacted AgI suggested that a thin layer of solid silver forming at AgI surface may evolve to be protective against transportation of reactant species, which can lead to the depression in the dissolution of AgI.

On the Adsorption Capability of Powder Activated Carbon for Phenol

2014 ◽  
Vol 709 ◽  
pp. 422-425
Author(s):  
Shao Fen Zhong ◽  
Jian Wen Mo ◽  
Yang Ping Li
Keyword(s):  
Activated Carbon ◽  
High Performance ◽  
Solid Phase ◽  
Pure Water ◽  
Equilibrium Concentration ◽  
Impact Factors ◽  
Raw Water ◽  
Adsorption Model ◽  
Powder Activated Carbon ◽  
Adsorption Capability

Using solid phase extraction and high performance liquid chromatography (HPLC), this paper studies the adsorption capability of activated carbon to phenol. The phenol wastewater is simulated with raw water and pure water, respectively. In detail, we examine impact factors including adsorption time, activated carbon dosage, equilibrium concentration of phenol. Using the adsorption principles from the aspect of kinetics, our study shows that adsorption of powder activated carbon to phenol conforms to the Fran Delhi Freundrich adsorption model.

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