Magnetite

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

Magnetic properties of dredged oceanic gabbros and the source of marine magnetic anomalies

Abstract: Summary. Magnetic property studies (natural remanent magnetization, initial susceptibility, progressive alternating field demagnetization and magnetic mineralogy of selected samples) were completed on 45 samples of gabbro and metagabbro recovered from 14 North Atlantic ocean-floor localities. The samples are medium to coarse-grained gabbro and metagabbro which exhibit subophitic intergranular to hypidiomorphic granular igneous textures. The igneous mineralogy is characterized by abundant plagioclase, varying amounts of clinopyroxene and hornblende, and lesser amounts of magnetite, ilmenite and sphene. Metamorphic minerals (actinolite, chlorite, epidote and fine-grained alteration products) occur in varying amounts as replacement products or vein material. The opaque mineralogy is dominated by magnetite and ilmenite. The magnetite typically exhibits a trellis of exsolution-oxidation ilmenite lamellae that appears to have formed during deuteric alteration. The NRM intensities of the gabbros range over three orders of magnitude and give a geometric mean of 2.8 x 10-4gau~~ and an arithmetic mean of 8.8 x 10-4gauss. The Konigsberger ratio, a measure of the relative importance of remanent to induce magnetization, is greater than unity for the majority of the samples and indicates that remanent magnetization on average dominates the total magnetization of oceanic gabbros in the Earth's magnetic field. The magnetic properties of fresh and metamorphosed gabbros appeared to be similar. The majority of gabbros studied were characterized by median destructive fields greater than 200 Oe. The high stability is attributed largely to the effective subdivision of the magnetite grains by the

Fabrication and Characterization of SiO2/(3-Aminopropyl)triethoxysilane-Coated Magnetite Nanoparticles for Lead(II) Removal from Aqueous Solution

Abstract: A novel nano-adsorbent SiO2/(3-aminopropyl)triethoxysilane-coated magnetite nanoparticles was synthesized for the adsorption of lead ions from water samples. Its structure and magnetic characteristics were characterized, by FTIR, powder X-ray diffraction, scanning electron microscope (SEM), transmission electron microscope (TEM) and vibrating sample magnetometry (VSM). Amino-functionalized SiO2 coated Fe3O4 magnetite nano-adsorbent exhibited superparamagnetic behavior and strong magnetization at room temperature. The efficiency of the nano-adsorbent in separation of the metals was evaluated by adsorption technique. Kinetic data were analyzed using the pseudo-first-order and pseudo-second-order equations. The data fitted very well to the pseudo-second-order kinetic model.The linear Langmuir and Freundlich models were applied to describe equilibrium isotherms and Langmuir model fitted well. The monolayer adsorption capacity was found as 17.65 mg/g at pH 4.0. Thermodynamic parameters such as free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were also calculated. These parameters showed that the adsorption of Pb(II) onto nano-adsorbent was feasible, spontaneous and endothermic. The amino-functionalized SiO2 coated Fe3O4 magnetic nano-adsorbent shows high adsorption capability for metal ions from aqueous solutions via the chelation mechanisms. The Pb(II) loaded nano-adsorbent can be easily recovered from aqueous solution with magnetic separation and regenerated readily by acid treatment. The product of this work can be used as an effective and recyclable nano-adsorbent for the removal of metal ions in wastewater treatment.

Nonredox transformations of magnetite-hematite in hydrothermal systems

Abstract: The transformation of magnetite to hematite, or hematite to magnetite, in nature has generally been considered a redox reaction and linked to a specific redox state of fluid; however, a nonredox reaction, Fe2O3 (hm) + Fe2+ + H2O = Fe3O4 (mt) + 2H+, may have been the principal mechanism for the transformations of iron oxides in nature, especially in hydrothermal environments. For example, the transformation of goethite and/or hematite (primary precipitates) to magnetite in banded iron-formations (BIFs) probably occurred through nonredox reactions with Fe2+-bearing hydrothermal fluids during the accumulation of a BIF sequence, rather than through redox reactions involving organic matter during and/or after the BIF deposition. The proposed mechanisms for the transformation of magnetite to hematite provides new exploration strategies for hematite-rich secondary ores, extending the target for orebodies to much deeper zones below the paleosurface. Another important implication of the proposed mechanism is that the presence or absence of magnetite and/or hematite in geologic formations may or may not provide meaningful information on the redox state of fluid.

Oxidation state and local structure of plutonium reacted with magnetite, mackinawite, and chukanovite.

Abstract: Due to their redox reactivity, surface sorption characteristics, and ubiquity as corrosion products or as minerals in natural sediments, iron(II)-bearing minerals control to a large extent the environmental fate of actinides. Pu-LIII-edge XANES and EXAFS spectra were used to investigate reaction products of aqueous 242Pu(III) and 242Pu(V) reacted with magnetite, mackinawite, and chukanovite under anoxic conditions. As Pu concentrations in the liquid phase were rapidly below detection limit, oxidation state and local structure of Pu were determined for Pu associated with the solid mineral phase. Pu(V) was reduced in the presence of all three minerals. A newly identified, highly specific Pu(III)-sorption complex formed with magnetite. Solid PuO2 phases formed in the presence of mackinawite and chukanovite; in the case of chukanovite, up to one-third of plutonium was also present as Pu(III). This highlights the necessity to consider, under reducing anoxic conditions, Pu(III) species in addition to tetravalen...