Magnetite

About: Magnetite is a research topic. Over the lifetime, 10277 publications have been published within this topic receiving 278071 citations.

The role of vanadium on the properties of iron based catalysts for the water gas shift reaction

Abstract: The substitution of chromium by vanadium as dopant in the iron oxide based water gas shift (WGS) catalyst has been investigated. Catalysts prepared as magnetite with different amount of vanadium have been prepared and tested with different amounts of water in the gas feed. The results obtained showed that vanadium was a promising dopant leading to very active and stable catalysts. The vanadium-doped catalysts have been characterized by means of chemical analysis, X-ray diffraction, Fourier transform infrared spectroscopy, specific surface area measurements, temperature-programmed reduction, Mossbauer spectroscopy, X-ray photoelectron spectroscopy and high resolution transmission electron microscopy with electron diffraction. Vanadium has been shown to be present both as V(III) and V(IV) species at the surface and in the bulk near the surface of the magnetite structure. It increased the specific surface area of the catalysts and kept the particles apart on the surface delaying sintering. The vanadium doping has been shown to have also an effect on the Fe(III) content of the magnetite which increased favoring the successive oxidation and reduction cycles, during the reaction.

Biotechnological application of nano-scale engineered bacterial magnetic particles

Abstract: Magnetic particles have been studied with much interest with reference to many engineering applications. Much effort has been devoted to the preparation of nano-sized magnetite particles with well-controlled size and shape. Magnetic bacteria synthesize uniform and nano-sized magnetite particles enveloped by organic lipid membranes. This review discusses recent advances in bacterial magnetite particles. Especially, the tremendous biotechnological potential of bacterial magnetite particles (BMPs) and our recent understanding of mechanism of magnetite particle formation in Magnetospirillum magneticum strain AMB-1 were highlighted.

Photocatalytic degradation of organics in water in the presence of iron oxides: Influence of carboxylic acids

Abstract: The effects of four carboxylic acids: malic, citric, tartaric and oxalic acids on the leaching of iron from two commercial iron oxides (hematite, α-Fe2O3, and magnetite, Fe3O4) have been investigated. The variables studied were the doses of iron oxides and carboxylic acids used as well as aqueous pH, temperature and the presence of hydrogen peroxide and/or UV-A radiation. On the whole, Fe3O4 led to higher amounts of leached iron than α-Fe2O3, and oxalic acid was the most effective carboxylic acid used. The importance of iron leaching has been considered to explain the photodegradation of bisphenol A (BPA) by UV-A/iron oxides systems. The influence of the presence of hydrogen peroxide and/or titania on the efficiency of these oxidation systems was also investigated. At the conditions tested, advanced oxidation with the UV-A/iron oxide/oxalic acid/H2O2/TiO2 system led to the lowest BPA half life (<15 min) among those processes studied.

Incorporation and Retention of 99-Tc(IV) in Magnetite under High pH Conditions

Abstract: Technetium incorporation into magnetite and its behavior during subsequent oxidation has been investigated at high pH to determine the technetium retention mechanism(s) on formation and oxidative perturbation of magnetite in systems relevant to radioactive waste disposal. Ferrihydrite was exposed to Tc(VII)(aq) containing cement leachates (pH 10.5-13.1), and crystallization of magnetite was induced via addition of Fe(II)aq. A combination of X-ray diffraction (XRD), chemical extraction, and X-ray absorption spectroscopy (XAS) techniques provided direct evidence that Tc(VII) was reduced and incorporated into the magnetite structure. Subsequent air oxidation of the magnetite particles for up to 152 days resulted in only limited remobilization of the incorporated Tc(IV). Analysis of both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data indicated that the Tc(IV) was predominantly incorporated into the magnetite octahedral site in all systems studied. On reoxidation in air, the incorporated Tc(IV) was recalcitrant to oxidative dissolution with less than 40% remobilization to solution despite significant oxidation of the magnetite to maghemite/goethite: All solid associated Tc remained as Tc(IV). The results of this study provide the first direct evidence for significant Tc(IV) incorporation into the magnetite structure and confirm that magnetite incorporated Tc(IV) is recalcitrant to oxidative dissolution. Immobilization of Tc(VII) by reduction and incorporation into magnetite at high pH and with significant stability upon reoxidation has clear and important implications for limiting technetium migration under conditions where magnetite is formed including in geological disposal of radioactive wastes.