Proportion Of Fe2 Research Articles

Dissecting the Photochemical Reactivity of Metal Ions during Atmospheric Nitrate Transformations on Photoactive Mineral Dust.

Dissecting the photochemical reactivity of metal ions is a significant contribution to understanding secondary pollutant formation, as they have a role to be reckoned with atmospheric chemistry. However, their photochemical reactivity has received limited attention within the active nitrogen cycle, particularly at the gas-solid interface. In this study, we delve into the contribution of magnesium ion (Mg2+) and ferric ion (Fe3+) to nitrate decomposition on the surface of photoactive mineral dust. Under simulated sunlight irradiation, the observed NOX production rate differs by an order of magnitude in the presence of Mg2+ (6.02 × 10-10 mol s-1) and Fe3+ (2.07 × 10-11 mol s-1). The markedly decreased fluorescence lifetime induced by Mg2+ and the change in the valence of Fe3+ revealed that Mg2+ and Fe3+ significantly affect the concentration of nitrate decomposition products by distinct photochemical reactivity with photogenerated electrons. Mg2+ promotes NOX production by accelerating charge transfer, while Fe3+ hinders nitrate decomposition by engaging in a redox cyclic reaction with Fe2+ to consume photogenerated carriers continuously. Furthermore, when Fe3+ coexists with other metal ions (e.g., Mg2+, Ca2+, Na+, and K+) and surpasses a proportion of approximately 12%, the photochemical reactivity of Fe3+ tends to be dominant in depleting photogenerated electrons and suppressing nitrate decomposition. Conversely, below this threshold, the released NOX concentration increases sharply as the proportion of Fe3+ decreases. This research offers valuable insights into the role of metal ions in nitrate transformation and the generation of reactive nitrogen species, contributing to a deep understanding of atmospheric photochemical reactions.

Paracetamol and Atenolol mitigation by Fenton and adsorption in-simultaneous process – Adsorbent regeneration and QSAR eco-toxicity prediction

This study aims to study the adsorption and oxidation of Paracetamol (PAR) and Atenolol (ATL) for application in water treatment. The pharmaceutical concentrations were monitored over time to assess the efficiency of the simultaneous process. The pH, contact time, and activated carbon (GAC) concentration were the variables evaluated in the adsorption process. While to the Fenton reaction, the proportion of Fe2+/H2O2 was the variable studied. Outcomes show that the most suitable conditions in the adsorption process to treat 40 mg/L of each pharmaceutical were achieved at 3 g of activated carbon (GAC) and 60 min.Tothe Fenton reaction, a ratio of 0.5 Fe2+/H2O2 was the most suitable condition. The results obtained in the simultaneous process were 17 % of mineralization, and 100 and 73.3 % of degradation of ATL and PAR. respectively. The formation of degradation products also decreased after treatment, suggesting the potential environmental safety of the combined treatment. A regeneration study was conducted to recuperate the GAC. The results showed that a GAC regeneration of 98 % was achieved after 4 cycles by the Fenton process, maintaining the degradation of pollutants evaluated at ∼ 99–98 %. Finally, a toxicity Quantitative Structure-Activity Relationship (QSAR) study was carried out to predict its potential toxicity, showing that it is feasible to conclude that the method has positive implications for environmental safety.

Saltwater intrusion increases phosphorus abundance and alters availability in coastal soils with implications for future sea level rise

Sea level rise (SLR) promotes saltwater intrusion (SWI) into coastal soils globally at an increasing rate, impacting phosphorus (P) dynamics and adjacent water quality. However, how SWI influences P molecular speciation and availability in coastal soils remains poorly understood. By using a space-for-time substitution strategy, we evaluated the SWI impacts on P transformation along a SWI gradient at the Rehoboth Inland Bay, which consists of five sampling locations along a transect representing different SWI degrees. Soils were analyzed at the macro- and micro-scale using X-ray absorption near edge spectroscopy (XANES) and the modified Hedley fractionation. With increasing distance from the Bay, soil salinity (29.3–0.07 mmhos cm−1), the proportion of Fe3+ to total Fe, and P concentrations decreased. The fractionation showed that recalcitrant P was dominant (86.9–89.5% of total P). With increasing SWI, labile P increased gradually, reached a plateau, and then decreased sharply. Bulk XANES spectroscopy showed that soil P was likely dominated by iron and aluminum-associated P (Fe/Al-P), regardless of the SWI degree. Hence, with increasing SWI, P increasingly accumulated in a recalcitrant pool, mainly as Fe/Al-P. μ-XANES spectroscopy revealed that calcium-associated P (Ca-P) existed in P-rich spots of the greatest SWI soil while Al-P occurred in P-rich spots of the low SWI soil, consistent with the greater HCl-P (presumably Ca-P) in the former soil. Overall, results demonstrate that SWI impacts P availability and environmental risk in coastal soils depending on the degree of SWI. These findings have important implications for understanding soil P cycling and availability in SLR-impacted coastal areas.

Oxalic acid enhanced ferrous/persulfate process for the degradation of triclosan in soil: Efficiency, mechanism and a column study

Triclosan (TCS) is a compound in pharmaceutical and personal care products (PPCPs) that preferentially accumulates in soil and may threaten human health. Iron-based persulfate activation processes (Fe-PAPs) are a promising technique in soil remediation but are limited by their narrow pH application range and resultant iron precipitation. In this study, oxalic acid (OA) was specifically introduced to improve the efficiency of Fe2+-activated persulfate (PS) processes for TCS degradation in soil. The complexation of OA and Fe2+ improved the total iron concentration in the Fe2+/OA/PS system and prevented iron precipitation. Fe-minerals in soil were also dissolved by OA, which participated in PS activation. The most appropriate proportion of Fe2+/OA/PS is 1:1:1, and approximately 85% of the TCS was degraded within 240 min compared with 45% in the Fe2+/PS system. SO4•- and 1O2 played important roles on TCS oxidation, while O2•- and CO2•- mainly participated in the iron cycle. The weak stretch of Fe-O in OA containing treatments in ATR-FTIR measurements provided evidence that OA dissolved the Fe-minerals. The introduction of OA in the Fe2+/PS system in four different soils reduced the negative effect of soil organic matter on TCS degradation. Three types of intermediates including hydroxylation, cleavage of ether bonds and cyclization products, were identified by LC-Q-TOF-MS. Column experiments were used to study the feasibility of in situ chemical oxidation (ISCO) remediation of TCS in the Fe2+/OA/PS system. Our findings indicated the ability of OA to be used as a cheating agent in Fe-PAPs for TCS soil remediation.

Stability and bioaccessibility of iron in pumpkin discs vacuum impregnated with ferrous gluconate, β-cyclodextrin and ascorbic acid

Present work evaluates the content and bioaccessibility of iron in vacuum-cooked pumpkin discs (VCPD) impregnated with ferrous gluconate (FeGlu) solutions added with β-cyclodextrin (BCD) and/or ascorbic acid (AA). The stability of Fe2+, AA and color of the VCPD after refrigerated storage were also studied. Pumpkin discs treated with any of the FeGlu studied solutions reached a total iron content between 17 and 20 mg Fe2+/100 g. Addition of BCD or AA to FeGlu solution improved Fe2+ of VCPD compared to control fortified only with FeGlu. After in vitro digestion, soluble Fe2+ was also significantly higher in pumpkins impregnated with BCD and AA solutions. Both BCD and AA probably exert their positive effect favoring the solubility of iron and/or the stability of the ferrous iron form, being the bioaccessibility of Fe2+ approximately 17 and 20% w/w respectively, and 10% for the FeGlu-impregnated discs. Although BCD did not have the impact observed for AA, a synergistic effect was observed in BCD-FeGlu-AA systems, where the proportion of Fe2+ was approximately 50% higher than in FeGlu after 21 days of refrigerated storage. The use of BCD and AA also allowed to better maintain the color of the fortified pumpkin discs after cooking and refrigerated storage.

Sensitive colorimetric glucose sensor by iron-based nanozymes with controllable Fe valence.

The proportion of Fe2+ and Fe3+ in Fe-based nanozymes is a key point in determining their catalytic activity. However, it is hard to adjust the Fe2+/Fe3+ ratio in nanozyme systems to achieve the best catalytic performance. In this work, we successfully regulate Fe2+/Fe3+ ratios in a wide range of 0.81-1.45 based on a novel porous platform of Fe doped silica hollow spheres. The homogeneous distribution and stable fixation of Fe components in Fe doped silica hollow spheres facilitate the valence regulation of Fe in the reduction heating in H2/Ar. When the Fe doped spheres (FeOx@SHSs) were used as nanozymes, different Fe2+/Fe3+ ratios have shown to influence the peroxidase-like catalytic activity greatly. The highest activity at the ratio of 1.41 should be due to the combined effects of the accelerated reaction rate by Fe2+ and the enhanced catalytic cycle efficiency by Fe3+. The FeOx@SHSs-based nanozyme is further applied to construct a facile colorimetric biosensing system, which exhibited extremely sensitive determination of glucose. This work presents an effective platform for controlling Fe valences and optimizing the peroxidase-like activity for catalytic processes or sensing systems.

Characterization and functional application of PrBa0.5Sr0.5Co1.5Fe0.5O5+δ cathode material for IT-SOFC

The physicochemical properties for layered perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) oxide are systematically investigated to gain insight into the correlation between structure, surface state and oxygen reduction reaction properties. The PBSCF sample possesses orthorhombic structure and keeps better structural stability under operating conditions. X-ray photoelectron spectra analysis indicates that the mixed oxidation state of (Co, Fe) and Pr promotes the oxygen reduction reaction kinetics by creating oxygen vacancies at the surface. Mössbauer Spectroscopy affirms that the proportion of Fe3+ and Fe4+ in iron species is 79.1 % and 20.9 %, respectively. The electrode polarization resistance is 0.067 Ω cm2 at 800 °C in air. The oxygen-ion bulk diffusion plays the rate-limiting step during the electrode process. The cell with PBSCF cathode delivers the power density of 590 mW cm−2 at 800 °C. These results show the PBSCF exhibits a promising application prospect in intermediate temperature solid oxide fuel cell.

Synthesis, Elasticity, and Spin State of an Intermediate MgSiO3‐FeAlO3 Bridgmanite: Implications for Iron in Earth's Lower Mantle

AbstractFe‐Al‐bearing bridgmanite may be the dominant host for ferric iron in Earth's lower mantle. Here we report the synthesis of (Mg0.5Fe3+0.5)(Al0.5Si0.5)O3 bridgmanite (FA50) with the highest Fe3+‐Al3+ coupled substitution known to date. X‐ray diffraction measurements showed that at ambient conditions, the FA50 adopted the LiNbO3 structure. Upon compression at room temperature to 18 GPa, it transformed back into the bridgmanite structure, which remained stable up to 102 GPa and 2,600 K. Fitting Birch‐Murnaghan equation of state of FA50 bridgmanite yields V0 = 172.1(4) Å3, K0 = 229(4) GPa with K0′ = 4(fixed). The calculated bulk sound velocity of the FA50 bridgmanite is ~7.7% lower than MgSiO3 bridgmanite, mainly because the presence of ferric iron increases the unit‐cell mass by 15.5%. This difference likely represents the upper limit of sound velocity anomaly introduced by Fe3+‐Al3+ substitution. X‐ray emission and synchrotron Mössbauer spectroscopy measurements showed that after laser annealing, ~6% of Fe3+ cations exchanged with Al3+ and underwent the high‐ to low‐spin transition at 59 GPa. The low‐spin proportion of Fe3+ increased gradually with pressure and reached 17–31% at 80 GPa. Since the cation exchange and spin transition in this Fe3+‐Al3+‐enriched bridgmanite do not cause resolvable unit‐cell volume reduction, and the increase of low‐spin Fe3+ fraction with pressure occurs gradually, the spin transition would not produce a distinct seismic signature in the lower mantle. However, it may influence iron partitioning and isotopic fractionation, thus introducing chemical heterogeneity in the lower mantle.

Effect of additives on stabilization and inhibition of mercury re-emission in simulated desulphurization slurry

The introduction of additives into desulfurization slurry may inhibit the mercury re-emission from slurry and improve the stabilization of mercury in slurry. In this paper, the effect of common additives, such as sodium sulfide (Na2S), 2,4,6-trimercaptotriazine trisodium (TMT-18), sodium dithiocarbamate (DTCR-2) and Fenton reagent, on mercury distribution in gas–liquid–solid phase was investigated under typical operating conditions. Meanwhile, the effect of different additive dosages on the inhibition performance of mercury re-emission was studied. Furthermore, the inhibition mechanisms of different additives were also discussed. The experimental results showed that Na2S, TMT-18, DTCR-2 and Fenton reagent could inhibit the mercury re-emission from desulfurization slurry and some mercury that might reemit into the gas phase before would be restrained in the solid phase. For additives such as Na2S, TMT-18 and DTCR-2, with the increase in additive dosages, the inhibition performances of mercury re-emission were improved, but the enhancing effects tended to level off. More mercury could be restrained in the solid phase by forming HgS, Hg-TMT and Hg-DTCR. However, for additives such as Fenton reagent, the inhibition performance of mercury re-emission was first increased and then decreased with the proportion of Fe2+ and H2O2 in Fenton reagent increasing. There existed an optimal proportion. The oxygenated free radical generated by Fenton reagent with Fe2+ as catalysis was the main reason for the inhibition of mercury re-emission, and more mercury would be oxidized and then restrained in solid phase due to the formation of HgSO4 and Fe(OH)3.

Partitioning of indium between ferromagnesian minerals and a silicate melt

Indium demand has increased with the development of new 21st century technologies. The association of indium deposits with felsic igneous rocks suggests a need for increased research on the behavior of indium in magmatic-hydrothermal systems. In order to better understand the relationship between igneous processes and the formation of indium-bearing deposits, experiments have been conducted at 750 and 800 °C and 100 MPa to constrain the partitioning of indium between ferromagnesian (biotite and amphibole) minerals and felsic melts. The partition coefficient DInBt/Melt ranges from 0.6 ± 0.1 (1 σm (standard deviation of the mean)) to 16 ± 3 (1 σm). The variation in DInBt/Melt is a function of XAnniteBt (the proportion of Fe2+ in the octahedral site), tetrahedral aluminum, and titanium, such that DInBt/Melt decreases with increasing XAnniteBt, tetrahedral aluminum, and titanium. DInAmp/Melt has a mean of 36 ± 4 (1 σm) and composition has only a minor effect on the magnitude of DInAmp/Melt. Additionally, an aqueous volatile phase was recovered from select experiments, which provides an initial constraint on DInVapor/Melt. DInVapor/Melt can be influenced by the chlorine content of both the vapor and melt, and is estimated to be ~17 ± 5 (1 σm). Theoretical considerations suggest that DInBt/Melt can be affected above and beyond the effect of XAnniteBt by water fugacity and the activity of the sanidine component in the system. Theoretical considerations suggest that DInAmp/Melt can be affected by the activities of diopside, anorthite, and enstatite in the system and the fugacity of water. These results suggest that the amount of magmatically-derived indium available for ore formation is a function of the proportion of ferromagnesian minerals in the crystallization products of the magma.

Influence of Organic Ligands on the Surface Oxidation State and Magnetic Properties of Iron Oxide Particles

Abstract For the application of iron oxide nanoparticles from thermal decomposition approaches as contrast agents in magnetic resonance imaging (MRI), their initial hydrophobic ligands have to be replaced by hydrophilic ones. This exchange can influence the surface oxidation state and the magnetic properties of the particles. Here, the effect of the anchor group of three organic ligands, citric acid and two catechols, dihydrocaffeic acid and its nitrated derivative nitro dihydrocaffeic acid on iron oxide nanoparticles is evaluated. The oleate ligands of Fe3O4/γ-Fe2O3 nanoparticles prepared by the thermal decomposition of iron oleate were exchanged against the hydrophilic ligands. X-ray absorption spectroscopy, especially X-ray magnetic circular dichroism (XMCD) measurements in the total electron yield (TEY) mode was used to investigate local magnetic and electronic properties of the particles’ surface region before and after the ligand exchange. XMCD was combined with charge transfer multiplet calculations which provide information on the contributions of Fe2+ and Fe3+ at different lattice sites, i.e. either in tetrahedral or octahedral environment. The obtained data demonstrate that nitro hydrocaffeic acid leads to least reduction of the magnetizability of the surface region of the iron oxide nanoparticles compared to the two other ligands. For all hydrophilic samples, the proportion of Fe3+ ions in octahedral sites increases at the expense of the Fe2+ in octahedral sites whereas the percentage of Fe3+ in tetrahedral sites hardly changes. These observations suggest that an oxidation process took place, but a selective decrease of the Fe2+ ions in octahedral sites ions due to surface dissolution processes is unlikely. The citrate ligand has the least oxidative effect, whereas the degree of oxidation was similar for both catechol ligands regardless of the nitro group. Twenty-four hours of incubation in isotonic saline has nearly no influences on the magnetic properties of the nanoparticles, the least on those with the nitrated hydrocaffeic acid ligand.

Characterization of the magnetic entropy of double perovskite (Sr1.55Gd0.15Ba0.3)FeMoO6

Double perovskite compounds Sr2FeMoO6 (SFMO) and (Sr1.55Gd0.15Ba0.3)FeMoO6 (SGBFMO) are prepared by standard solid-state reaction. X-ray powder diffraction patterns show that both samples crystallize in the single phase, and they belong to the I4/m space group. The Fe/Mo orders η are 91.7 (3)% for SFMO and 86.2 (3)% for SGBFMO. The Curie temperatures (TC) are 394 K for SFMO and 382 K for SGBFMO. The maximum entropy changes are |SMmax| = 2.13 J K−1 kg−1 for SFMO at 394 K and |SMmax| = 1.98 J K−1 kg−1 for SGBFMO at 382 K |SMmax| decreases, but the curve of magnetic entropy change (MEC) becomes broader for SGBFMO. The proportions of Fe3+/Fe2+ and Mo5+/Mo6+ in SFMO are 2.190121 and 2.022055, respectively, whereas those in SGBFMO are 1.130396 and 3.295191, respectively. Sufficiently large spontaneous magnetization and abrupt drop in magnetization at TC are the two necessary prerequisites for large MEC.

Opaque Mineralogy as a Tracer of Magmatic History of Volcanic Rocks: an Example from the Neogene‐Quaternary Harrat Rahat Intercontinental Volcanic Field, North Western Saudi Arabia

Abstract:The Neogene‐Quaternary Harrat Rahat volcanic field is part of the major intercontinental Harrat fields in western Saudi Arabia. It comprises lava flows of olivine basalt and hawaiite, in addition to mugearite, benmorite, and trachyte that occur mainly as domes, tuff cones and lava flows. Based on opaque mineralogy and mineral chemistry, the Harrat Rahat volcanic varieties are distinguished into Group I (olivine basalt and hawaiite) and Group II (mugearite, benmorite and trachyte). The maximum forsterite content (∼85) is encountered in zoned forsteritic olivine of Group I, whereas olivine of Group II is characterized by intermediate (Fo=50), fayalitic (Fo=25) and pure fayalite in the mugearite, benmorite and trachyte, respectively. The more evolved varieties of Group II contain minerals that show enrichment of Fe2+, Mn2+ and Na+ that indicates normal fractional crystallization. The common occurrence of coarse apatite with titanomagnetite in the benmorite indicates that P5+ becomes saturated in this rock variety and drops again in trachyte. Cr‐spinel is recorded in Group I varieties only and the Cr# (0.5) suggests lherzolite as a possible restite of the Harrat Rahat volcanics. The plots of Cr# vs. the forsterite content (Fo) suggest two distinct trends, which are typical of mixing of two basaltic magmas of different sources and different degrees of partial melting. The bimodality of Harrat Rahat Cr‐spinel suggests possible derivation from recycled MORB slab in the mantle as indicated by the presence of high‐Al spinel. It is believed that the subcontinental lithospheric mantle was modified by pervious subduction process and played the leading role in the genesis of the Harrat Rahat intraplate volcanics. The trachytes of the Harrat Rahat volcanic field were formed most probably by melting of a lower crust at the mantle‐crust boundary. The increase in fO2 causes a decrease in Cr2O3, and Al2O3, and a strong increase in the proportion of Fe3+ and Mg# of spinel crystallizing from the basaltic melt at T ∼1200°C. The olivine‐pyroxene and olivine‐spinel geothermometers yielded equilibrium temperature in the range of 935–1025°C, whereas the range of <500–850°C from single‐pyroxene thermometry indicates either post crystallization re‐equilibrium of the clinopyroxene, or the mineral is xenocrystic and re‐equilibrated in a cooling basaltic magma.

Study on Coloration Mechanism of Chinese Ancient Ceramics by X-ray Absorption Near-edge Structure

The Fe K-edge X-ray absorption near-edge structure (XANES) spectra of a series of ceramic shards were measured by fluorescence mode to reveal the color-generating techniques of Chinese porcelain. The analysis disclosed relationships among the chemical form of the iron, the firing conditions and the colors of the ceramics. The results indicate that the coloration for different ceramics depend on the valence states of iron as the main color element in glaze and the proportion of Fe2+ and Fe3+ was attributed to the baking technology. The findings provide important information for archaeologist on the coloration researches.

Coordination and RedOx ratio of iron in sodium‐silicate glasses

Mössbauer and Electron paramagnetic resonance (EPR) spectroscopy studies of iron status in doped sodium-silicate glasses (100−x, mol%)Na2O(x, mol%)SiO2(y, wt.%) Fe2O3 (x=75; 81; y=0.05–13) were made as a function of glass matrix and total iron content.55Total iron content is expressed as Fe2O3 in the paper. Mössbauer spectroscopy identified three signals: Fe3+ doublet, Fe2+ doublet and Fe3+ broad hyperfine splitting (HFS) at room temperature dealing with slow relaxation effect of ferric ions. X-band EPR spectra exhibits resonance signals at g≈2.0, g≈4.3 and a shoulder in the region of g≈6.0. EPR spectra were simulated on the basis of rhombic spin-Hamiltonian with Zeeman and fine-structure terms. The nature of EPR absorption signals was interpreted as a combination of five types of Fe3+ complexes. Three of them were clustered ferric ions and two others were isolated paramagnetic ferric ions in distorted octahedral sites. The iron RedOx ratio (Fe2+/Fe3+) has been estimated from Mössbauer spectroscopy, while proportion of Fe3+ ions in adjacent sites (Fe3+isolated)/Fe3+clustered) has been obtained from Mössbauer spectra and simulated EPR spectra.

Preparation and Photo-Catalysis Properties of Fe<sub>3</sub>O<sub>4</sub>/TiO<sub>2</sub> Nanocomposite

As a Kind of Most Common Used Photocatalyst, TiO2 Nanomaterials Existing Disadvantages on Low Light Energy Utilization in Visible Light Range and Difficulty on Recycle. in Our Study, Different Proportions of Fe3+ and Fe2+ Ion Were Doped with Nano-Ti02 Particles in Structure of Rutile Type through Method of Chemical Precipitation. the Result Showed that Nano-Composites Formed by TiO2 Coexist with Fe3O4, with the Average Size of the Composite Particles Nearly 20 Nm. the Photo-Catalyst Performances of the Composite Have Improved Largely, and so the Relatively Optimized Preparation Conditions Were Presented.

MIL03346, the most oxidized Martian meteorite: A first look at spectroscopy, petrography, and mineral chemistry

Meteorite MIL03346, recovered from Antarctica, is a nakhlite: an augite clinopyroxenite inferred to have originated from Mars' surface. MIL03346 contains ∼70% augite and 3% olivine in a fine‐grained mesostasis of basaltic glass, olivine, titanomagnetite, and pyrrhotite. Part of the olivine is altered to fine‐grained ferric clays and oxides: “iddingsite” as described in other nakhlites. Chemical compositions of augite and olivine (FeO/MnO and Fe/Mg) are nearly identical to those of other nakhlites and are consistent with a Martian origin. The augite contains significant Fe3+: ∼24% of total iron by Mössbauer spectroscopy and ∼13% by elemental analyses and crystal chemistry. This proportion of Fe3+ in augite is consistent with high‐temperature equilibration near the QFM oxygen buffer. Thermal emission spectra are similar to those of other nakhlites. Visible to mid‐IR spectra of MIL03346 show the same absorption features as do other nakhlites but at distinctly lower reflectances (which likely represent Fe3+ in augite and magnetite). MIL03346 appears to contain the most Fe3+ of any Martian meteorite studied to date and to have come from the most oxidizing magmatic environment yet reported.

Effect of the Tetrahedral Charge on the Order-Disorder of the cation Distribution in the Octahedral Sheet of Smectites and Illites by Computational Methods

AbstractThe order-disorder behavior of the isomorphous cation substitution of the octahedral sheet of phyllosilicates was investigated by Monte Carlo simulations based only on atomistic models in some three-species systems Al/Fe/Mg including a wide range of different octahedral compositions that can be relevant to clay compositions found in nature, especially for smectites and illites. In many cases, phase transitions do not occur, in that long-range order is not attained, but most systems exhibit short-range order at low temperature. The ordering of the octahedral cations is highly dependent on the cation composition. Variations in the tetrahedral charge (smectite vs. illite) produce slight differences in the cation distribution and the short-range and long-range order of octahedral cations do not change drastically. The average size of Fe clusters and the long-range order of Fe are not larger in illites than in smectites as previous reports concluded, but the proportion of Fe3+ cations non-clustered is higher in smectites than in illites. This behavior supports the experimental behavior of the Fe effect on the Al-NMR signal, which is lower in illites than in smectites.

The influence of humic substances on the molecular weight distributions of phosphate and iron in epilimnetic lake waters

1. The influence of humic substances on the association of free inorganic iron and phosphate with material of larger molecular weight was investigated in epilimnetic samples from two humus‐rich lakes of contrasting ionic strength. After modification of the molecular weight distribution of the humic substances in the samples using dialysis and ultrafiltration, the molecular weight distribution of added radioisotopes ( Fe3+ and PO43−) was assessed using gel filtration chromatography. 2. The association of Fe3+ and PO43− with larger molecular weight fractions (>50 000 and 10 000–50 000 Da) was not in general related to the quantity of humic substances of the same molecular weight in the samples. However, the proportions of Fe3+ and PO43− observed in higher molecular weight peaks were strongly correlated to the quantity of humic substances of the same molecular weight in (a) the 10 000–50 000 Da peak in the sample of low ionic strength at pH 5.5 and pH 7.0, and (b) the> 50 000 Da peak in the sample of higher ionic strength at pH 4.0. 3. It was concluded that humic substances promote the association of Fe3+ and PO43− with higher molecular weight fractions primarily by acting as peptizing agents for inorganic colloids containing Fe and P. Association of Fe3+ and PO43− with material of higher molecular weight via the formation of humic substance‐Fe3+–PO43− complexes was identified but only at specific pH and within specific molecular weight ranges for each of the epilimnetic lake water samples studied.

Bound iron admixture prevents the spontaneous generation of peroxides in total parenteral nutrition solutions.

Parenteral administration of iron is a matter of controversy because it is feared that it could contribute to oxidative reactions. The aim of this study was to verify if irondextran participates in the redox reactions occurring in total parenteral nutrition (TPN) solutions. Irondextran was compared with different forms of iron in the interaction with peroxides. Hydroperoxide levels were measured by a colorimetric technique in TPN solutions, in presence of varying sources (FeCl2, FeSO4, irondextran, iron sorbitol) and concentrations (0-0.8 mM) of iron. The consumption and inhibition of peroxide generation were tested by analyzing the effect of iron on different sources of peroxides (H2O2, tert-butyl and cumen hydroperoxide). The free radicals produced under conditions of a Fenton-like reaction were measured by the oxidation of scopoletin. And the proportion of Fe3+ freed by both bound-iron sources was counted by measuring the masking effect on the thiol function of cysteine. Free-iron admixture to parenteral nutrition induces the formation of free radicals, whereas sources of bound-iron inhibit the generation of peroxides in parenteral nutrition without implying a Fenton-like reaction. For patients requiring iron supplementation, bound-iron should be added during the preparation of TPN solutions, because it protects against the spontaneous generation of peroxides.