Adsorption of arsenite and arsenate on amorphous iron hydroxide

Adsorption isotherms in solutions with ionic strengths of 0.01 at 25°C were measured over the arsenite and arsenate concentration range 10−7−10−3 M and the pH range 4–10. At low concentrations, these isotherms obeyed equations of the Langmuir type. At higher concentrations the adsorption isotherms were linear, indicating the existence of more than one type of surface site on the amorphous iron hydroxide adsorbent. Removal of arsenite and arsenate by amorphous iron hydroxide throughout the concentration range were determined as a function of pH. By careful selection of the relative concentration of arsenic and amorphous iron hydroxide and pH, removals on the order of 92% can be achieved.

Iron oxyhydroxide nanostructured in montmorillonite clays: Preparation and characterization

Akaganeite is a very rare iron oxyhydroxide in nature. It can be obtained by many synthetic routes, but thermohydrolysis is the most common method reported in the literature. In this work, akaganeite-like materials were prepared through the thermohydrolysis of FeCl(3)center dot 6H(2)O in water and suspensions containing clay minerals. X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) data show that the clays determine the crystal phase and size of the iron oxyhydroxide crystals. According to XRD and FTIR data, beta-FeO(OH) (akaganeite) is the main metal oxyhydroxide phase. Considering the small basal spacing (d(0 0 1)) displacement observed when comparing the XRD patterns of pristine clays with the composites containing beta-FeO(OH), the iron oxyhydroxide should be mostly located on the basal and edge surfaces of the clay minerals. UV-Vis electronic absorption spectra indicate that the preferred phase of the iron oxyhydroxide is determined by the nature of the clay minerals. (C) 2010 Elsevier Inc. All rights reserved.

Morphological Evolution in Air-Stable Metallic Iron Nanostructures and Their Magnetic Study

Iron nanostructures with morphology ranging from discrete nanoparticles to nearly monodisperse hierarchical nanostructures have been successfully synthesized using solvated metal atom dispersion (SMAD) method. Such a morphological evolution was realized by tuning the molar ratio of ligand to metal. Surface energy minimization in confluence with strong magnetic interactions and ligand-based stabilization results in the formation of nanospheres of iron. The as-prepared amorphous iron nanostructures exhibit remarkably high coercivity in comparison to the discrete nanoparticles and bulk counterpart. Annealing the as-prepared amorphous Fe nanostructures under anaerobic conditions affords air-stable carbon-encapsulated Fe(0) and Fe3C nanostructures with retention of the morphology. The resulting nanostructures were thoroughly analyzed by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and Raman spectroscopy. TGA brought out that Fe3C nanostructures are more robust toward oxidation than those of a-Fe. Finally, detailed magnetic studies were carried out by superconducting quantum interference device (SQUID) magnetometer and it was found that the magnetic properties remain conserved even upon exposure of the annealed samples to ambient conditions for months.

A detailed study of the lithiation of iron phosphate as well as the development of a novel synthesis of lithium iron silicate as cathode material for lithium-ion batteries

Dans cette thèse nous démontrons le travail fait sur deux matériaux de cathodes pour les piles lithium-ion. Dans la première partie, nous avons préparé du phosphate de fer lithié (LiFePO4) par deux méthodes de lithiation présentées dans la littérature qui utilisent du phosphate de fer (FePO4) amorphe comme précurseur. Pour les deux méthodes, le produit obtenu à chaque étape de la synthèse a été analysé par la spectroscopie Mössbauer ainsi que par diffraction des rayons X (DRX) pour mieux comprendre le mécanisme de la réaction. Les résultats de ces analyses ont été publiés dans Journal of Power Sources. Le deuxième matériau de cathode qui a été étudié est le silicate de fer lithié (Li2FeSiO4). Une nouvelle méthode de synthèse a été développée pour obtenir le silicate de fer lithié en utilisant des produits chimiques peu couteux ainsi que de l’équipement de laboratoire de base. Le matériau a été obtenu par une synthèse à l’état solide. Les performances électrochimiques ont été obtenues après une étape de broyage et un dépôt d’une couche de carbone. Un essai a été fait pour synthétiser une version substituée du silicate de fer lithié dans le but d’augmenter les performances électrochimiques de ce matériau.

Geochemistry of iron and manganese in soils and sediments of a mangrove system, Island of Pai Matos (Cananeia - SP, Brazil)

Five zones along a transect of 180 m were selected for study on the Island of Pai Matos (Sao Paulo, Brazil). Four of the zones are colonised by vascular plants (Spartina SP, Laguncularia LG, Avicennia AV and Rhizophora RH) and were denominated soils, and the other zone, which lacks vegetation, was denominated sediment (SD). The geochemical conditions differed significantly in soils and sediment and also at different depths. The soils were oxic (Eh > 350 mV) or suboxic (Eh: 350-100 mV) at the surface and anoxic (Eh < 100 mV) at depth, whereas in the sediment anoxic conditions prevailed at all depths, but with a lower concentration of sulphides in the pore water and pyrite in the solid fraction. Under these geochemical conditions Fe is retained in the soils, while the Mn tends to be mobilized and lost. The most abundant form of iron oxyhydroxide was lepidocrocite (mean concentration for all sites and depths, 45 +/- 19 mu mol g(-1)), followed by goethite (30 19 mu mol g(-1))and ferrihydrite (19 +/- 11 mu mol g(-1)),with significant differences among the mean concentrations. There was a significant decrease with depth in all the types of Fe oxyhydroxides measured, particularly the poorly crystalline forms. The pyrite fraction was an important component of the free Fe pool (non-silicate Fe) in all soils as well as in the sediment, especially below 20 cm depth (mean concentration for all sites and depths, 60 +/- 54 mu mol CI). Furthermore, the mean concentration of Fe-pyrite for all sites and depths was higher than that obtained for any of the three Fe oxyhydroxides measured. The Fe-AVS was a minor fraction, indicating that the high concentrations of dissolved Fe in the soils in the upper area of the transect result from the oxidation of Fe sulphides during low tide. Mossbauer spectroscopy also revealed that most of the Fe (III) was associated with silicates, in this case nontronite. The presence of crystals of pyrite associated with phyllosilicates in samples from the upper layer of the soils may indicate that pyritization of this form of Fe(III) is more rapid than usually reported for ocean bed sediments. The sequential extraction of Mn did not reveal any clearly dominant fraction, with the Mn-carbonate fraction being the most prevalent, followed by exchangeable Mn and oxides of Mn, whereas pyrite-Mn and Mn associated with crystalline Fe-oxides were present at significantly lower concentrations. The high concentration of dissolved Mn found in the soils in the lower part of the transect is consistent with the fact that the solubility is determined by the carbonate fraction. Unlike for Fe, in the soils in the higher zone, which are subject to intense drainage during low tide, there was loss of Mn, as reflected by the concentration of total Mn. (C) 2008 Elsevier B.V. All rights reserved.

Degradation of hydroxycinnamic acid mixtures in aqueous sucrose solutions by the Fenton process

The degradation efficiencies and behaviors of caffeic acid (CaA), p-coumaric acid (pCoA) and ferulic acid (FeA) in aqueous sucrose solutions containing the mixture of these hydroxycinnamic acids (HCAs) mixtures were studied by the Fenton oxidation process. Central composite design and multi-response surface methodology were used to evaluate and optimize the interactive effects of process parameters. Four quadratic polynomial models were developed for the degradation of each individual acid in the mixture and the total HCAs degraded. Sucrose was the most influential parameter that significantly affected the total amount of HCA degraded. Under the conditions studied there was < 0.01% loss of sucrose in all reactions. The optimal values of the process parameters for a 200 mg/L HCA mixture in water (pH 4.73, 25.15 °C) and sucrose solution (13 mass%, pH 5.39, 35.98 °C) were 77% and 57% respectively. Regression analysis showed goodness of fit between the experimental results and the predicted values. The degradation behavior of CaA differed from those of pCoA and FeA, where further CaA degradation is observed at increasing sucrose and decreasing solution pH. The differences (established using UV/Vis and ATR-FTIR spectroscopy) were because, unlike the other acids, CaA formed a complex with Fe(III) or with Fe(III) hydrogen-bonded to sucrose, and coprecipitated with lepidocrocite, an iron oxyhydroxide.

Single crystalline magnetite, maghemite, and hematite nanoparticles with rich coercivity

One-pot synthesis of amorphous iron oxide nanoparticles with two different dimensions (<5 nm and 60 nm) has been achieved using the reverse micelle method, with <5 nm nanoparticles separated from the stable colloid by exploiting their magnetic behaviour. The transformation of the as-prepared amorphous powders into Fe3O4 and Fe2O3 phases (gamma and alpha) is achieved by carrying out controlled annealing at elevated temperatures under different optimized conditions. The as-prepared samples resulting from micellar synthesis and the corresponding annealed ones are thoroughly characterized by powder X-ray diffraction, transmission electron microscopy (TEM), and by Raman and X-ray photoelectron spectroscopies. Expectedly, the magnetic characteristics of Fe3O4 and Fe2O3 phase (gamma and alpha) nanoparticles are found to have strong dependence on their phase, dimension, and morphology. The coercivity of Fe3O4 and Fe2O3 (gamma and alpha) nanoparticles is reasonably high, even though high resolution TEM studies bring out that these nanoparticles are single crystalline. This is in contrast with previous reports wherein poly-crystallinity of iron oxides nanoparticles has been regarded as a prerequisite for high coercivity.

中太平洋海区富钴结壳地球化学特征及成因机制

本文利用ICP-AES、EPMA、X-ray衍射等测试技术以及聚类分析和因子分析等多种数理统计方法，系统地对中太平洋海区富钴结壳的元素地球化学特征、矿物组成和微观组构进行了研究，并探讨了其成因机制，获得以下主要认识： 1中太平洋海区富钴结壳类型多样，均为水成成因，其矿物相主要由锰矿物相、铁矿物相和非金属矿物相组成；富钴结壳壳层发育多种原生和次生构造类型。 2磷酸盐化作用不仅强烈改变富钴结壳元素初始含量，而且造成富钴结壳某些元素间的相关性发生改变，这些敏感型元素对可用于指示富钴结壳是否发生磷酸盐化。在不同水深段内，未磷酸盐化型富钴结壳的主要元素随经向、纬向的变化趋势相似，表明其受水体化学障、表面生产力和物质来源等环境参数控制；而随水深的变化则具有区域一致性，表明水体化学具有区域成层性。 3未磷酸盐化富钴结壳稀土元素含量和轻重稀土分馏程度随水深发生规律变化，这种变化不仅与它们在海洋中的含量和行为有关，也与海洋背景颗粒的吸附有关；铈(Ce)在富钴结壳中基本上呈4价，且动力学因素控制了其富集过程，因此Ce异常不能用于指示富钴结壳形成环境的氧化程度。 4基于富钴结壳微层呈锯齿状且同一微层生长速率不同，提出了富钴结壳在各种基底表面生长以及后继发育过程受固液界面双电层控制的发育模式。在富钴结壳整个发育过程中，经历了从贫氧环境向富氧环境的转变，但微环境则呈富氧-低氧过程的交替。 关键词： 富钴结壳；中太平洋；元素地球化学；界面双电层

Haematite in Lateritic Soils Aids Groundwater Disinfection

Microbiologically contaminated water severely impacts public health in low-income countries, where treated water supplies are often inaccessible to much of the population. Groundwater represents a water source that commonly has better microbiological quality than surface water. A 2-month intensive flow and quality monitoring programme of a spring in a densely settled, unsewered parish of Kampala, Uganda, revealed the persistent presence of high chloride and nitrate concentrations that reflect intense loading of sewage in the spring’s catchment. Conversely, thermotolerant coliform bacteria counts in spring water samples remained very low outside of periods of intense rainfall. Laboratory investigations of mechanisms responsible for this behavior, achieved by injecting a pulse of H40/1 bacteriophage tracer into a column packed with locally derived granular laterite, resulted in near-total tracer adsorption. X-ray diffraction (XRD) analysis showed the laterite to consist predominantly of quartz and kaolinite, with minor amounts (<5%) of haematite. Batch studies comparing laterite adsorption capacity with a soil having comparable mineralogy, but with amorphous iron oxide rather than haematite, showed the laterite to have a significantly greater capacity to adsorb bacteriophage. Batch study results using pure haematite confirmed that its occurrence in laterite contributes substantially to micro-organism attenuation observed and serves to protect underlying groundwater.

Does ochre have the potential to be a remedial treatment for As-contaminated soils?

Ochre is an iron oxyhydroxide-rich waste that accumulates in water bodies associated with disused mines. Laboratory experiments were conducted to examine the potential of four different ochres to be used as remedial agents for As contaminated soils. The ochres removed As from solution (200 and 500 mg L−1) in adsorption experiments at pH 3 and 8 and, when added to As contaminated soil (5% w/w) significantly reduced As release to solution. In both these experiments the highest surface area ochres performed best. The impact of ochre amendments on uptake of As from soil by plants and humans and release of As to ground water was assessed in a year-long incubation study. Ochres increased soil pH and reduced CaCl2 extractable As but had no consistent effect on plant growth, plant As uptake or As extraction in physiologically-based extraction tests. Ochre may be better used for water treatment than soil remediation.

Bário, cádmio, cromo e chumbo em plantas de milho e em Latossolo que recebeu lodo de esgoto por onze anos consecutivos

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Analysis of biogenic magnetite nanoparticles

Cobalt doped magnetite (CoxFe3-xO4) nanoparticles have been produced through the microbial reduction of cobalt-iron oxyhydroxide by the bacterium Geobacter sulfurreducens. The materials produced, as measured by SQUID, x-ray magnetic circular dichroism, Mössbauer spectroscopy, etc., show dramatic increases in coercivity with increasing cobalt content without a major decrease in overall saturation magnetization. Structural and magnetization analyses reveal a reduction in particle size to <4 nm at the highest Co content, combined with an increase in the effective anisotropy of the magnetic nanoparticles. The potential use of these biogenic nanoparticles in aqueous suspensions for magnetic hyperthermia applications is demonstrated. Further analysis of the distribution of cations within the ferrite spinel indicates that the cobalt is predominantly incorporated in octahedral coordination, achieved by the substitution of Fe2+ site with Co2+, with up to 17 per cent Co substituted into tetrahedral sites.

Sesquióxidos de hierro en bosques templado húmedos del estado de Hidalgo, México

Se estudian las formas de hierro extraídas con oxalato ácido de amonio, pirofosfato de sodio, ditionito-citrato-bicarbonato, así como el hierro total en disolución en suelos Alisoles en el municipio de Acaxochitlán, Hidalgo, México. Los suelos estudiados soportan distintos tipos de vegetación forestal: Pinus patula Schlecht and Cham (Pp), Pinus teocote, (Pt) y Quercus spp, (Q). El objetivo del trabajo fue determinar si la vegetación influye significativamente sobre las diferentes fracciones de hierro (Fe) en el suelo. Los contenidos de Fe total son significativamente mayores en suelos bajo vegetación de Pp (14,5% de Fe2O3), el mayor porcentaje de ferrihidrita (38,0% del Fe total en suelo) y de complejos organominerales de Fe y óxidos amorfos de Fe (20,9% y 16,3% respectivamente del Fe total en suelo, se dio en el bosque de Pt. En los suelos bajo bosques de Pp predominaron formas de Fe lábil (56,7% del Fe total en suelo) y formas cristalinas de Fe (goetita/hematita). La vegetación de Q mostró mayor alteración de los suelos y en el caso de Pt y Pp se presentó una mayor evolución en el proceso de organización estructural de los oxihidróxidos de Fe. El tipo de vegetación forestal influye en el grado de evolución del suelo, y en la distribución, contenido y formas de óxidos de Fe. En un orden de mayor a menor el contenido de Fe total en el suelo fue Pinus patula > Quercus spp > Pinus teocote.