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.

scholarly journals Morpho-Mineralogical and Bio-Geochemical Description of Cave Manganese Stromatolite-Like Patinas (Grotta del Cervo, Central Italy) and Hints on Their Paleohydrological-Driven Genesis

2021 ◽  
Vol 9 ◽  
Author(s):  
Simone Bernardini ◽  
Fabio Bellatreccia ◽  
Andrea Columbu ◽  
Ilaria Vaccarelli ◽  
Marika Pellegrini ◽  
...  
Keyword(s):  
Microbial Communities ◽  
Oxidation State ◽  
Central Italy ◽  
Analytical Techniques ◽  
Local Environment ◽  
Fine Grained ◽  
Average Oxidation State ◽  
Hydraulic Regime ◽  
Subsurface Environments ◽  
Cave Environment

Caves are dark subsurface environments with relatively constant temperatures that allow studying bio-mineralization processes and paleoenvironmental or climate changes in optimal conditions. In the extreme and oligotrophic cave environment, manganese patinas having stromatolite-like features are uncommon. Here we provide the first detailed mineralogical, geochemical, and microbiological investigation of fine-grained and poorly crystalline MnFe stromatolite-like wall patinas formed in a deep-cave environment in Italy. These mineralizations, about 3 mm thick, consist of an alternation of Mn-layers and Fe-lenses. We show that the microbial communities' composition is dominated by Mn-oxidizing bacteria, such as Bacillus, Flavobacterium, and Pseudomonas. Our multidisciplinary investigation, integrating data from different analytical techniques (i.e., optical microscopy, SEM-EDS, μXRF, XRPD, FT-IR, Raman spectroscopy, and DNA sequencing), revealed peculiar chemical, mineralogical, and biological features: 1) A cyclical oscillation of Mn and Fe along the growth of the patinas. We propose that this oscillation represents the shift between oxic and suboxic conditions related to different phases occurring during paleo-flood events; 2) A typical spatial distribution of mineralogy and oxidation state of Mn, bacterial imprints, detrital content, and stromatolite-like morphologies along the Mn-layers. We propose that this distribution is controlled by the local hydraulic regime of the paleo-floods, which, in turn, is directly related to the morphology of the wall surface. Under less turbulent conditions, the combination of clay mineral catalysis and biological oxidation produced vernadite, a poor-crystalline phyllomanganate with a low average oxidation state of Mn, and branched columnar stromatolite-like morphologies. On the other hand, under more turbulent conditions, the sedimentation of clay minerals and microbial communities' development are both inhibited. In this local environment, a lower oxidation rate of Mn2+ favored the formation of todorokite and/or ranciéite, two compounds with a high average oxidation state of Mn, and flat-laminated or columnar stromatolite-like morphologies.

Point Defect Properties from Metal Diffusion Experiments — What Does the Data Really Tell Us?

1997 ◽  
Vol 469 ◽  
Author(s):  
Srinivasan Chakravarthit ◽  
Scott T. Dunham
Keyword(s):  
Point Defect ◽  
Equilibrium Concentration ◽  
Simulation Software ◽  
Published Data ◽  
Vacancy Diffusion ◽  
Metal Diffusion ◽  
Float Zone ◽  
Equilibrium Concentrations ◽  
Parameter Values ◽  
Carbon Concentrations

Point defect properties, including diffusivities and equilibrium concentrations for both interstitials and vacancies, are commonly extracted from metal diffusion experiments, and these values are widely used in process simulation software. However, in many cases, these parameter values were extracted using oversimplified models which ignore interactions between interstitial and vacancy diffusion mechanisms. Questions about the accuracy of these parameters have come from ab-initio defect calculations which conclude that vacancies diffuse faster than interstitials, in contrast with published reports on metal diffusion which find vacancies diffuse much more slowly than interstitials. We have reanalyzed published data for zinc and platinum diffusion and find that it is possible to match all of the data using fast vacancy diffusivity. The most direct evidence for slow vacancy diffusion (and a high equilibrium concentration) comes from platinum diffusion experiments. However, we are able to reproduce these results with fast V diffusion and carbon/interstitial clustering, using carbon concentrations typical of Czochralski and float zone silicon (1016cm−3). We evaluate the effectiveness of metal diffusion experiments in determining point defect parameters, and find that it is not possible to reliably determine both diffusivities and equilibrium concentrations for both interstitials and vacancies from metal diffusion results.

scholarly journals Polyaspartate-Ionene/Na+-Montmorillonite Nanocomposites as Novel Adsorbent for Anionic Dye; Effect of Ionene Structure

Polymers ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 2843
Author(s):  
Hany El-Hamshary ◽  
Abeer S. Elsherbiny ◽  
Mohamed H. El-Newehy ◽  
Mohamed E. EL-Hefnawy
Keyword(s):  
Adsorption Isotherm ◽  
Antimicrobial Agents ◽  
Organic Pollutant ◽  
Bet Surface Area ◽  
Sodium Montmorillonite ◽  
Freundlich Model ◽  
Intraparticle Diffusion Model ◽  
Pseudo Second Order ◽  
Kinetics Of ◽  
Acid Blue

Surface modification of sodium montmorillonite (Na+-Mt) was performed using antimicrobial agents to produce an ecofriendly nanocomposite. The adsorption performance of the nanocomposite has been evaluated for the removal of Acid Blue 25 dye (AB25) as a model organic pollutant from wastewater. Sodium montmorillonite (Na+-Mt) was modified with three different ionene compounds through ion exchange, and further modified through reaction with polyaspartate to provide three ecofriendly nanocomposites (denoted ICP-1–3). The nanocomposites were characterized using FTIR, PXRD, TEM, SEM, and BET surface area. The adsorption isotherm of AB25 onto ICP-1, ICP-2 and ICP-3 was analyzed using the Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) models. The adsorption isotherm was found to be best fitted by a Freundlich model. The thermodynamic parameters were calculated. The kinetics of the adsorption data were analyzed and the adsorption behavior was found to obey pseudo-second-order kinetics, and the intraparticle diffusion model. The adsorption mechanism was studied by FTIR.

Dissolution kinetics of meta-torbernite under circum-neutral to alkaline conditions

2009 ◽  
Vol 6 (6) ◽  
pp. 551 ◽  
Author(s):  
Dawn M. Wellman ◽  
Bruce K. McNamara ◽  
Diana H. Bacon ◽  
Elsa A. Cordova ◽  
Ruby M. Ermi ◽  
...  
Keyword(s):  
Dissolution Kinetics ◽  
Coupled Processes ◽  
Effect Of Temperature ◽  
Subsurface Environments ◽  
Alkaline Conditions ◽  
Flow Through ◽  
Uranium Phosphate ◽  
The Stability ◽  
Kinetics Of

Environmental context. Uranium-phosphate minerals have been identified as a long-term controlling phase that limit the mobility of uranium to groundwater in many contaminated subsurface environments. Complex, coupled processes confound the ability to isolate the rates attributed to individual processes. Results of this investigation provide the necessary information to refine current prediction on the release and long-term fate of uranium in subsurface environments. Abstract. The purpose of this investigation was to conduct a series of single-pass flow-through (SPFT) tests to (1) quantify the effect of temperature (23–90°C) and pH (6–10) on meta-torbernite dissolution; (2) compare the dissolution of meta-torbernite to other autunite-group minerals; and (3) evaluate the effect of aqueous phosphate on the dissolution kinetics of meta-torbernite. Results presented here illustrate meta-torbernite dissolution rates increase by ~100× over the pH interval of 6 to 10, irrespective of temperature. The power law coefficient for meta-torbernite, η = 0.59 ± 0.07, is greater than that quantified for Ca-meta-autunite, η = 0.42 ± 0.12. This suggests the stability of meta-torbernite is greater than that of meta-autunite, which is reflected in the predicted stability constants. The rate equation for the dissolution of meta-torbernite as a function of aqueous phosphate concentration is log rdissol (mol m–2 s–1) = –4.7 × 10–13 + 4.1 × 10–10[PO43–].

Assessment of the Public Radiation Protection and Economic Activity Safety in the Area of the Developed Uranium Deposit

2020 ◽  
Vol 65 (2) ◽  
pp. 11-16
Author(s):  
A. Titov ◽  
N. Shandala ◽  
D. Isaev ◽  
M. Semenova ◽  
V. Seregin ◽  
...  
Keyword(s):  
Economic Activity ◽  
Equilibrium Concentration ◽  
Dose Equivalent ◽  
Economic Activities ◽  
The Public ◽  
Equivalent Rate ◽  
Ambient Dose Equivalent ◽  
Equilibrium Concentrations ◽  
Effective Doses ◽  
The Town

Purpose: To analize radiation situation in the vicinity of mine number one of the Lermontov Production Association “Almaz” in the areas of the public residence and economic activities. Material and methods: During the study, methods of pedestrian gamma surveys with a portable spectrometric complex MKS-01A “Multirad-M” and short-term measurements of radon equivalent equilibrium concentration with aerosol alpha radiometer RAA-20P2 “Poisk” were used. Results: Along the main roads used by the population for walks and rest, the values of the gamma ambient dose equivalent rate vary within the range between 0.10 and 0.86 μSv/h. Local areas with excess of the remediation criterion (0.6 μSv / h), established by the Sanitary Rules for elimination, conservation and changing functions of facilities for radioactive ore mining and milling (SP LKP-91), are located on the ascent of Beshtau Mountain from the side of the Town of Pyatigorsk (near tunnels and dumps). Along other routes, the remediation criteria are met. External effective doses to the population in a single passage of the routes vary from 1.0 to 1.6 µSv. The highest contribution to the dose from manmade radiation does not exceed 30 %. The highest external doses (4.3 μSv at the contribution of manmade radiation about 70 %) can be realized when resting near the most contaminated parts of the dumps or tunnel mouths. The equivalent equilibrium concentrations of radon progenies in air along the routes did not exceed 60 Bq/m3. The effective internal dose due to inhalation intake of radon and its progenies will not exceed 3 μSv when single passing routes. Conclusions: In the main areas of the residence and economic activity of the population in the vicinity of mine number 1 , the radiation situation at some locations does not comply with the requirements of the SP LKP-9, however, it does not pose a threat to public health.

Adsorption of toluene from the mixed water−toluene system on medicinal activated carbon

2014 ◽  
Vol 92 (5) ◽  
pp. 392-396
Author(s):  
Igor Winkler ◽  
Volodymyr Diychuk
Keyword(s):  
Experimental Investigation ◽  
Activated Carbon ◽  
Adsorption Kinetics ◽  
Surface Adsorption ◽  
Equilibrium Concentration ◽  
Coal Surface ◽  
Adsorption Model ◽  
Insufficient Amount ◽  
Mixed Water ◽  
Kinetics Of

An experimental investigation of adsorption of toluene from the aqueous phase on medicinal activated carbon revealed that the process runs by the mechanism of preactivated adsorption. Kinetics of the initial stages of adsorption can be adequately represented by the empirical Elovich adsorption model. An insufficient amount of the adsorbent can cause an unexpected jump in the toluene equilibrium concentration in water caused by transferring this substance from the toluene phase into water through the process of additional adsorption on the coal surface. Adsorption constants and “imaginary” adsorption values have been determined for a series of toluene contents.

The kinetics of iodide oxidation by the manganese oxide mineral birnessite

2009 ◽  
Vol 73 (10) ◽  
pp. 2850-2861 ◽  
Author(s):  
Patricia M. Fox ◽  
James A. Davis ◽  
George W. Luther
Keyword(s):  
Manganese Oxide ◽  
Oxide Mineral ◽  
Iodide Oxidation ◽  
Kinetics Of ◽  
Manganese Oxide Mineral

Rapid determination of the Mn average oxidation state of Mn oxides with a novel two-step colorimetric method

2017 ◽  
Vol 9 (1) ◽  
pp. 103-109 ◽  
Author(s):  
Yanhua Zhu ◽  
Xinran Liang ◽  
Huaiyan Zhao ◽  
Hui Yin ◽  
Mingming Liu ◽  
...  
Keyword(s):  
Trace Metals ◽  
Oxidation State ◽  
Organic Contaminants ◽  
Rapid Determination ◽  
Colorimetric Method ◽  
Oxidation Processes ◽  
Average Oxidation State ◽  
Mn Oxides

The Mn average oxidation state (Mn AOS) of Mn oxides has a significant impact on their reactivity towards trace metals and organic contaminants via sorption, catalysis and oxidation processes.

scholarly journals On the kinetics of organic pollutant degradation with Co2+/peroxymonosulfate process: When ammonium meets chloride

Chemosphere ◽  
2017 ◽  
Vol 179 ◽  
pp. 331-336 ◽  
Author(s):  
Ying Huang ◽  
Fei Yang ◽  
Luoyan Ai ◽  
Min Feng ◽  
Chi Wang ◽  
...  
Keyword(s):  
Organic Pollutant ◽  
Pollutant Degradation ◽  
Organic Pollutant Degradation ◽  
Kinetics Of
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