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Abstract  

Samples of magnetite, prepared by standard methods for obtaining of melted ammonia synthesis catalysts have been studied. The samples contain small amounts of additives, such as K2O (0.4–1 mass%), CaO (0.7–1.5 mass%), Al2O3 (0–2 mass%), WO3 (0–1 mass%) and MoO3 (0–0.6 mass%). Some influences of the additives to magnetite, as well as formation of other individual phases were established.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: P. Nayak, D. Das, S. Chintalapudi, P. Singh, S. Acharya, V. Vijayan, and V. Chakravortty

Abstract  

Two representative titaniferous magnetite samples procured from Moulabhanj, Orissa, India have been studied by PIXE, EDXRF, Mössbauer spectroscopy, and XRD techniques. Major iron-bearing phases identified in the samples by Mössbauer spectroscopy and XRD are magnetite, hematite, ferrous ilmenite and ferric ilmenite. The Fe2+/Fe3+ ratio and the relative percentages of different minerals were determined from the resonance areas of Mössbauer spectra. Quantitative multielemental analysis was carried out by energy dispersive X-ray fluorescence (EDXRF) and proton induced X-ray emission (PIXE). Nineteen minor and trace elements have been quantified by EDXRF whereas by PIXE eighteen elements have been analyzed quantitatively. Concentrations of trace elements determined by EDXRF and PIXE were used in interpreting the physico-chemical condition of the depositional basin.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Debasish Das, M. Sureshkumar, Siddhartha Koley, Nidhi Mithal, and C. Pillai

Abstract  

Magnetite (Fe3O4) nanoparticle was synthesized using a solid state mechanochemical method and used for studying the sorption of uranium(VI) from aqueous solution onto the nanomaterial. The synthesized product is characterized using SEM, XRD and XPS. The particles were found to be largely agglomerated. XPS analysis showed that Fe(II)/Fe(III) ratio of the product is 0.58. Sorption of uranium on the synthesized nanomaterials was studied as a function of various operational parameters such as pH, initial metal ion concentration, ionic strength and contact time. pH studies showed that uranium sorption on magnetite is maximum in neutral solution. Uranium sorption onto magnetite showed two step kinetics, an initial fast sorption completing in 4–6 h followed by a slow uptake extending to several days. XPS analysis of the nanoparticle after sorption of uranium showed presence of the reduced species U(IV) on the nanoparticle surface. Fe(II)/Fe(III) ratio of the nanoparticle after uranium sorption was found to be 0.48, lower than the initial value indicating that some of the ferrous ion might be oxidized in the presence of uranium(VI). Uranium sorption studies were also conducted with effluent from ammonium diuranate precipitation process having a uranium concentration of about 4 ppm. 42% removal was observed during 6 h of equilibration.

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Abstract  

Black sands originating from north, west and south seaside strips of the Bay of Burgas, Black Sea, were investigated. It was found that these sands are martitized magnetites. Their composition involves mixtures of nonstoichiometric magnetite and maghemite or stoichiometric magnetite and hematite.

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Journal of Thermal Analysis and Calorimetry
Authors: Oana Carp, Luminita Patron, Daniela Culita, Petru Budrugeac, Marcel Feder, and Lucian Diamandescu

Abstract  

The thermal stability of two kinds of dextran-coated magnetite (dextran with molecular weight of 40,000 (Dex40) and 70,000 (Dex70)), obtained by dextran adsorption onto the magnetite surface is investigated in comparison with free dextran in air and argon atmosphere. The thermal behavior of the two free dextran types and corresponding coated magnetites is similar, but atmosphere dependent. The magnetite catalyzes the thermal decomposition of dextran, the adsorbed dextran displaying lower initial decomposition temperatures comparative with the free one in both working atmospheres. The dextran adsorbed onto the magnetite surface decomposes in air through a strong sharp exothermic process up to ~450 °C while in argon atmosphere two endothermic stages are identified, one in the temperature range 160–450 °C and the other at 530–800 °C.

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Abstract  

The thermal stability of two amino acid-(tyrosine and tryptophan) coated magnetite and their corresponding precursors, [Fe2 IIIFeII(Tyr)8]·9H2O and [Fe2 IIIFeII(Trp)2(OH)4](NO3)2·8H2O (where tyrosine=Tyr and tryptophan=Trp), was analyzed in comparison with free amino acids. The complexes present a lower thermal stability relative to the free ligand, due to the catalytic effect introduced by the iron cation and the presence of NO3 groups. The presence of NO3 group determines also a different degradation’s stoichiometry of the amino acid anion comparative with the one expressed by the free ligand molecule. The amino acid bonded to magnetite decomposes in two steps, its presence inducing an increasing of γ-Fe2O3→Fe2O3 conversion temperature.

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Abstract  

The aim of the present study was to determine the kinetic equations for the thermal transformations of precipitated iron oxides and hydroxides, namely for the process of thermal dehydroxylation of goethite and consecutive of hematite crystal structure growth as well as for the oxidation of magnetite to maghemite and its thermal transformation into crystalline hematite. The investigations have been carried out using thermogravimetry (TG/DTG/DTA), X-ray powder diffractometry (XRD) and high temperature powder diffractometry (HT-XRD). This presentation contains the continuation of our earlier works.

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Abstract  

Kinetics of the oxidation of magnetite (Fe3O4) to hematite (a-Fe2O3) are studied in air using simultaneous TG/DSC. The mechanism is complex and the differences between the kinetic conclusions and Arrhenius parameters based on either TG or DSC are discussed. As in our previous work on CaCO3 [1], the determination of a satisfactory baseline for the DSC results adds considerable uncertainty to those kinetic results. Consequently the calculations based on the TG data are considered superior. Solid state reactivity varies from one source of material to another and the results are compared for two different commercial samples of magnetite, both presumably prepared by wet chemical methods. These materials are much more reactive than the material studied previously [2], which had been coarsened and refined at high temperatures. In that earlier study, the metastable spinel, g-Fe2O3, was formed as an intermediate in the oxidation to the final stable form, a-Fe2O3. The exothermic reaction of the gamma to alpha form of the product during the oxidation process destroys the direct comparison between the TG and DSC results, since the former only detects the change in mass of the sample and not the crystallographic transformation. The TG results, however, represent the true oxidation process without superposition of the structural aspects.

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Summary  

Potassium nickel hexacyanoferrate composite with magnetite finds application in the recovery of cesium from low-level liquid waste using magnetic assistance. The apparent sorption capability of hexacyanoferrate-magnetite composite and potassium nickel(II) hexacyanoferrate(II) matched indicating no loss in sorption capability as a consequence of coating to nanoscale magnetite substrate. Selectivity for cesium in a broad pH range, selectivity in the presence of high concentration of sodium nitrate, and fast exchange kinetics are additional features of the nanocomposites.

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Kinetics of low temperature hydrogen reduction of the metastable spinels

Magnetite and solid solutions with Mn, Co, Ni and Cu

Journal of Thermal Analysis and Calorimetry
Authors: D. Drakshayani and R. Mallya

Abstract  

The kinetics of reduction at relatively low temperatures with hydrogen of pure and doped metastable non-stoichiometric magnetite with 1 at% Mn, Co, Ni and Cu and also with 5 at % Ni and Cu have been investigated by using isothermal thermogravimetry in the temperature range 300–400°C. With increase in the concentration of the dopant (5 at% Ni and Cu), the reactivity increases. The activation energies for pure magnetite varies from 7 to 9 kcal/mole with the preparation temperature of precursorf Fe2O3 (250–400°C), being the lowest for those prepared at the lowest temperatures. The corresponding activation energies for the reduction of doped samples (Fe, M)3−zO4, it depends, apart from their porosity and surface areas, on the nature of the solute atom, amount of disorder, whether it occupies the tetrahedral (A) or octahedral (B) sites in the non-stoichiometric spinel and possibly on hydrogen ‘Spill over’ effects.

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