Mössbauer spectroscopy of green shale from banded iron formation

A green shale from the Precambrian banded iron formation of the Bonai Range, Eastern India, is examined by transmission Mössbauer spectroscopy. The constituent phases are identified to be chlorite, siderite and magnetite. The fractional resonance area of each constituent is computed and the ferrous-ferric ratio determined. The variation of this ratio over the sample is examined. Intensity of the magnetite lines reveals that deviation from stoichiometry is negligible. The observations suggest a transition within short range from silicate-rich facies to carbonate-oxide-rich facies in the studied section.     

Kinetics of low temperature hydrogen reduction of the metastable spinels

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.     

Removal of Lead(II), Cadmium(II), and Arsenic(III) from Aqueous Solution Using Magnetite Nanoparticles Prepared by Green Synthesis with Box–Behnken Design

Two types of magnetite (Fe₃O₄) nanoparticles were investigated as adsorbents for the simultaneous removal of Pb(II), Cd(II), and As(III) metal ions from aqueous solution. Magnetite nanoparticles were prepared by two synthesis procedures, both using water as solvent, and are referred to as conventional Fe₃O₄ nanoparticles and green Fe₃O₄ nanoparticles. The latter used Citrus limon (lemon) aqueous peel extract as the surfactant. Box–Behnken experimental design was used to investigate the effects of parameters such as initial concentration (20–150?mg?L^?1), pH (2–9), and biomass dosage (1–5?g?L^?1) on the removal of Pb(II), Cd(II), and As(III) ions. The optimum parameters for removal of the studied metal ions from aqueous solutions, including the initial ion concentration (20?mg?L^?1), pH (5.5) and adsorbent dose (5?g?L^?1), were determined. The pseudosecond-order model exhibited the best fit for the kinetic studies, while adsorption equilibrium isotherms were best described by Langmuir and Freundlich models. The optimum conditions were applied for the treatment wastewater. The removal efficiencies of Pb(II), Cd(II), and As(III) using the conventional and green synthesized Fe₃O₄ nanoparticles were 59.4?±?4.3, 18.7?±?1.9 and 17.5?±?1.6, and 98.8?±?5.6, 46.0?±?1.3, and 48.2?±?2.6%, respectively. These results demonstrate the potential of magnetite nanoparticles synthesized using C. limon peel extract as highly efficient adsorbents for the removal of Pb(II), Cd(II), and As(III) ions from aqueous solution.     

Oxidative Dehydrogenation of 1-Butene Over Magnetite

Magnetite (FC₃O₄), a partially reduced iron oxide, has long been considered as inactive in the oxidative dehydrogenation of butene. By studying a clean Fe₃O₄ powder, we found that Fe₃O₄, similar to other spinel ferrites, is not only active, but also more active and selective than α-Fe₂O₃. The active site densities and the desorption temperatures of oxidation products on Fe₃O₄ were also measured. Fe₃O₄ is, however, unstable under flow reaction conditions. Even if the bulk of the oxide is stabilized in the form of Fe₃O₄ at high temperatures and low O₂/C₄ ratios, its surface is gradually oxidized to a form close to α-Fe₂O₃, resulting in a decrease in both the activity and selectivity. The restructuring of the FC₃O₄ surface is temperature dependent. At 300°C, the high selectivity and activity of a low-surface-area Fe₃O₄ can be long preserved even if the bulk is oxidized to α-Fe₂O₃.     

Catalytic activity of aluminium and copper-doped magnetite in the high temperature shift reaction

Aluminium and copper-doped magnetite was evaluated as high temperature shift catalyst and compared with a hematite-based sample. The first one is less active but can save energy in industrial processes. This revised version was published online in June 2006 with corrections to the Cover Date.