scholarly journals How does silica affect Fe(II)-catalysed transformation of ferrihydrite and lepidocrocite?

2020 ◽  
Author(s):  
Katrin Schulz ◽  
Laurel Kathleen ThomasArrigo ◽  
Katherine Ann Rothwell ◽  
Ruben Kretzschmar
Keyword(s):  
Iron Atom ◽  
Solid Phase ◽  
Transformation Process ◽  
Soil Conditions ◽  
Natural Soil ◽  
X Ray Diffraction ◽  
Mineral Transformation ◽  
Iron Mineral ◽  
Mineral Phases ◽  
Reducing Conditions

<p>Ferric iron (Fe(III)) minerals, such as ferrihydrite and lepidocrocite, can be reduced to ferrous iron (Fe(II)) through microbial reductive dissolution under reducing soil conditions, to form dissolved Fe(II) or mixed Fe(II)-Fe(III) mineral phases. The dissolved Fe(II) catalyses iron mineral transformation to more crystalline iron phases. Silica (Si), in the form of silicic acid, is an ubiquitous component of natural soil solutions and is known to hinder the iron mineral transformation process. However, the mechanisms and the mineral phases that are formed during ferrihydrite and lepidocrocite transformation in the presence of Si remain unclear. We reacted ferrihydrite, Si-ferrihydrite co-precipitates, lepidocrocite and Si-adsorbed lepidocrocite with 0.3 mM and 3 mM isotopically labelled <sup>57</sup>Fe(II) for four weeks. At six time points, we sampled the solid and the aqueous phase, to follow iron mineral transformation by X-ray diffraction and dissolved Fe(II) dynamics. In addition, we tracked the iron atom exchange between the aqueous and the solid phase by measuring the <sup>57/56</sup>Fe isotope ratio in filtrates and dissolved solid phases. Our data demonstrates the hindering effect of Si on Fe(II) catalysed ferrihydrite and lepidocrocite transformation. The presence of Si decreased the initial Fe(II) adsorption and strongly slowed down the iron atom exchange, especially in the lepidocrocite treatment. Collectively, the results of this study demonstrate, how Si can impact iron mineral transformation in soils with different Fe(II) release potentials under reducing conditions.</p>

Efficient removal of antimony with natural secondary iron minerals: effect of structural properties and sorption mechanism

2020 ◽  
Vol 17 (4) ◽  
pp. 332
Author(s):  
Nana Wang ◽  
Nairui Deng ◽  
Yuyin Qiu ◽  
Zebin Su ◽  
Chujie Huang ◽  
...  
Keyword(s):  
Mine Drainage ◽  
Structural Characteristics ◽  
Anthropogenic Activities ◽  
Sorption Process ◽  
X Ray Diffraction ◽  
Iron Minerals ◽  
Iron Mineral ◽  
Mineral Phases ◽  
Maximum Sorption ◽  
The Relationship

Environmental contextAntimony is classified as a priority pollutant and is increasingly detected in the environment as a result of various anthropogenic activities. Natural secondary iron minerals are important sinks for many toxic elements. We found that antimony promotes structural transformations in secondary iron minerals, and that antimony is then further immobilised by the newly formed iron mineral phases. AbstractSecondary iron minerals (SIMs), naturally formed in acid mine drainage (AMD), can serve as sinks to remove antimony (Sb) from the environment. In this study, we investigated the relationship between the structural characteristics and SbIII or SbV sorption behaviours of two different SIMs (neo-formed SIM (n-SIM) and mature SIM (m-SIM)). The results showed that both m- and n-SIMs were composed of mixed crystal phases, mainly schwertmannite, jarosite, goethite and ferrihydrite. Despite similar elemental compositions, they had different microstructures. m-SIM was a regular spheroid with a close-packed arrangement, while n-SIM was an incomplete irregular spheroid with ordered channels and a random loose arrangement. The initial SbIII or SbV sorption rate order was n-SIM>m-SIM. The maximum sorption capacities of n- and m-SIMs were 219.8 (SbIII) or 366.3 (SbV) mg g−1 and 160.3 (SbIII) or 114.9 (SbV) mg g−1 respectively, and n- and m-SIMs could both effectively remove Sb from natural wastewaters, while trace Sb levels remained. Sb immobilisation on SIMs occurred as a rapid endothermal and homogeneous sorption process. After Sb sorption, the SO42− and total Fe(aq) concentrations in the sample solutions significantly changed. X-ray diffraction (XRD) and Raman analyses confirmed that n- or m-SIM had transformed in the presence of Sb, even without FeII(aq), which indicated an important SIMs transformation-Sb immobilisation relationship. These findings are valuable for better understanding the Sb behaviours associated with natural SIMs and the short-term fate of Sb in the environment.

scholarly journals First Report on the Geologic Occurrence of Natural Na–A Zeolite and Associated Minerals in Cretaceous Mudstones of the Paja Formation of Vélez (Santander), Colombia

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 218
Author(s):  
Carlos Alberto Ríos-Reyes ◽  
German Alfonso Reyes-Mendoza ◽  
José Antonio Henao-Martínez ◽  
Craig Williams ◽  
Alan Dyer
Keyword(s):  
Natural Zeolite ◽  
Scanning Electron Micrographs ◽  
Total Sulfur ◽  
Zeolite A ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mineral Phases ◽  
The World ◽  
Porosity And Permeability ◽  
First Time

This study reports for the first time the geologic occurrence of natural zeolite A and associated minerals in mudstones from the Cretaceous Paja Formation in the urban area of the municipality of Vélez (Santander), Colombia. These rocks are mainly composed of quartz, muscovite, pyrophyllite, kaolinite and chlorite group minerals, framboidal and cubic pyrite, as well as marcasite, with minor feldspar, sulphates, and phosphates. Total organic carbon (TOC), total sulfur (TS), and millimeter fragments of algae are high, whereas few centimeters and not biodiverse small ammonite fossils, and other allochemical components are subordinated. Na–A zeolite and associated mineral phases as sodalite occur just beside the interparticle micropores (honeycomb from framboidal, cube molds, and amorphous cavities). It is facilitated by petrophysical properties alterations, due to processes of high diagenesis, temperatures up to 80–100 °C, with weathering contributions, which increase the porosity and permeability, as well as the transmissivity (fluid flow), allowing the geochemistry remobilization and/or recrystallization of pre-existing silica, muscovite, kaolinite minerals group, salts, carbonates, oxides and peroxides. X-ray diffraction analyses reveal the mineral composition of the mudstones and scanning electron micrographs show the typical cubic morphology of Na–A zeolite of approximately 0.45 mμ in particle size. Our data show that the sequence of the transformation of phases is: Poorly crystalline aluminosilicate → sodalite → Na–A zeolite. A literature review shows that this is an unusual example of the occurrence of natural zeolites in sedimentary marine rocks recognized around the world.

scholarly journals Variation of the Chemical Composition of Waste Cooking Oils upon Bentonite Filtration

Resources ◽  
2019 ◽  
Vol 8 (2) ◽  
pp. 108 ◽  
Author(s):  
Alberto Mannu ◽  
Gina Vlahopoulou ◽  
Paolo Urgeghe ◽  
Monica Ferro ◽  
Alessandra Del Caro ◽  
...  
Keyword(s):  
Particle Size ◽  
Chemical Composition ◽  
Solid Phase ◽  
Volatile Fraction ◽  
X Ray Diffraction ◽  
Specific Chemical ◽  
Waste Cooking Oils ◽  
Main Components ◽  
Cooking Oils ◽  
Chemical Groups

The chemical composition and the color of samples of waste cooking oils (WCOs) were determined prior to and after filtration on two different pads of bentonite differing in particle size. The volatile fraction was monitored by headspace solid-phase microextraction (HS-SPME) coupled with gas-chromatography, while the variation of the composition of the main components was analyzed by 1H NMR. Both techniques allowed the detection of some decomposition products, such as polymers, terpenes, and derivatives of the Maillard process. The analysis of the chemical composition prior to and after bentonite treatment revealed a tendency for the clays to retain specific chemical groups (such as carboxylic acids or double bonds), independent of their particle size. A pair comparison test was conducted in order to detect the sensory differences of the intensity of aroma between the WCO treated with the two different bentonites. In addition, characterization of the bentonite by means of powder X-ray diffraction (XRD) and thermogravimetric measurements (TG) was performed.

Wide angle X-ray diffraction study of the solid-phase chlorinated poly(ethylene)

Polymer ◽  
2004 ◽  
Vol 45 (18) ◽  
pp. 6341-6348 ◽  
Author(s):  
S. Stoeva ◽  
A. Popov ◽  
R. Rodriguez
Keyword(s):  
Diffraction Study ◽  
Solid Phase ◽  
Wide Angle ◽  
X Ray Diffraction ◽  
X Ray ◽  
Poly Ethylene

Trapping Effect on the Kinetic Critical Radius in Nucleation and Growth Processes

2014 ◽  
Vol 790-791 ◽  
pp. 97-102
Author(s):  
Zoltán Erdélyi ◽  
Zoltán Balogh ◽  
Gabor L. Katona ◽  
Dezső L. Beke
Keyword(s):  
Critical Nucleus ◽  
Solid Phase ◽  
Kinetic Monte Carlo ◽  
Mean Field ◽  
Transformation Process ◽  
Nucleus Size ◽  
Critical Nucleus Size ◽  
Acta Mater ◽  
Order Of Magnitude ◽  
The Difference

The critical nucleus size—above which nuclei grow, below dissolve—during diffusion controlled nucleation in binary solid-solid phase transformation process is calculated using kinetic Monte Carlo (KMC). If atomic jumps are slower in an A-rich nucleus than in the embedding B-rich matrix, the nucleus traps the A atoms approaching its surface. It doesn’t have enough time to eject A atoms before new ones arrive, even if it would be favourable thermodynamically. In this case the critical nucleus size can be even by an order of magnitude smaller than expected from equilibrium thermodynamics or without trapping. These results were published in [Z. Erdélyi et al., Acta Mater. 58 (2010) 5639]. In a recent paper M. Leitner [M. Leitner, Acta Mater. 60 (2012) 6709] has questioned our results based on the arguments that his simulations led to different results, but he could not point out the reason for the difference. In this paper we summarize our original results and on the basis of recent KMC and kinetic mean field (KMF) simulations we show that Leitner’s conclusions are not valid and we confirm again our original results.

Combustion Synthesis of La0.65Sr0.35MnO3 and its Sensing Properties for NO2

2016 ◽  
Vol 680 ◽  
pp. 208-211
Author(s):  
Lian Lian Wu ◽  
Qiang Li ◽  
Dan Yu Jiang ◽  
Jin Feng Xia
Keyword(s):  
Solid Phase ◽  
High Sensitivity ◽  
Combustion Method ◽  
Fast Response ◽  
Size Analysis ◽  
Phase Method ◽  
X Ray Diffraction ◽  
Ultrafine Structure ◽  
Nox Sensor ◽  
Solid Phase Method

In this paper, La0.65Sr0.35MnO3 (LSM) oxide powder with ultrafine structure has been synthesized by self-propagating combustion method. The powders were characterized by X-ray diffraction, scanning electron microscopy and laser size analysis. Compared to the powders prepared by traditional solid-phase method, the grain size of powders prepared by self-propagating combustion method is relatively small and uniform. Starting from ultrafine LSM powders, sensing electrode (SE) for NO2 mixed-potential sensors based on yttria-stablized zirconia (YSZ) was fabricated. As-obtained NO2 sensor displays fast response and high sensitivity (25.4mV/decade). The response values of the sensor have good linear relationship with the logarithm of NO2 concentration varying from 30ppm to 500ppm.Keywords:Self-propagating combustion method; La0.65Sr0.35MnO3; NOx sensor; YSZ

PREPARATION OF ANTIMONY-PLATINUM SURFACE ALLOY ELECTRODE BY ATOM DIFFUSION IN THE SOLID PHASE

2006 ◽  
Vol 20 (25n27) ◽  
pp. 3999-4004
Author(s):  
HIROSHI MATSUI ◽  
KAZUFUMI WATANABE
Keyword(s):  
Diffraction Pattern ◽  
Low Temperatures ◽  
Solid Phase ◽  
Electrochemical Measurement ◽  
X Ray Diffraction ◽  
Platinum Surface ◽  
X Ray ◽  
Atom Diffusion ◽  
Heat Treated ◽  
Titanium Substrates

Antimony-platinum bilayers were prepared on titanium substrates by the two-step electrodeposition in the usual baths, and then surface alloys were formed by the atom diffusion in the solid phase. The simple antimony layer was little influenced by the substrate in both the measurements of X-ray diffraction and the i - E characteristic in a sulfuric acid solution. Regarding the bilayers, the catalytic activity in hydrogen evolution reaction was very sensitive to the presence of platinum, while the hydrogen adsorbability was quite insensitive. An interaction between antimony and platinum was confirmed by the appearance of a new dissolution wave in the electrochemical measurement and the occurrence of a new diffraction in the X-ray diffraction pattern after the heat-treatment of about 400°C. Although the new diffraction disagreed with any of the reported alloys, clear diffraction pattern of PtSb 2 alloy was observed, when the bilayers were heat-treated at about 600°C for one hour. Considering the penetration depth of X-ray, the alloying of antimony and platinum seems to occur also at low temperatures at least at the top surface.

Deterioration of concrete containing limestone powder exposed to sulfate attack at ambient temperature

2021 ◽  
Vol 11 (5) ◽  
pp. 724-731
Author(s):  
Hemin Liu ◽  
Qian Huang ◽  
Liang Zhao
Keyword(s):  
Ambient Temperature ◽  
Sulfate Solution ◽  
Sulfate Attack ◽  
Limestone Powder ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mineral Phases ◽  
Adverse Influence ◽  
Powder Content ◽  
Scanning Electron

This study investigates the deterioration of concrete containing limestone powder exposed to sulfate solution under ambient temperature (20~25 °C). Microstructure and mineral phases within the attacked concrete were measured by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). It was found that the addition of limestone powder increased the initial porosity of concrete. Consequently, a larger amount of SO2–4 ions diffused into the concrete containing limestone powder, and their degree of deterioration caused by sulfate attack increased with the increase in limestone powder content. At ambient temperature, gypsum and ettringite were the major attack products, respectively within the surface and nearsurface portions of concrete containing limestone powder, which was consistent with the products of sulfate attack within concrete without limestone powder. Therefore, the type and distribution of the attack products in concrete had not been revised due to the addition of limestone powder. Nevertheless, the adverse influence of limestone powder on the sulfate resistance of concrete, even at ambient temperature, should be considered. Furthermore, effective measures should be implemented to improve the durability of concrete containing limestone powder in this environment.

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