Magnetite iron effects

Pang, S.C., Chin, S.E, and Anderson, M.A., Redox equilibria of iron oxides in aqueous-based magnetite dispersions Effect of pH and redox potential, J. Colloid Interf. Sci., 311, 94, 2007. 

The mixed oxide Fc304 (tri-iron tetroxide) is a black solid, which occurs naturally as magnetite it is formed when iron(III) oxide is strongly heated, and its structure is effectively made up of oxide (O ) and iron(II) and iron(III) ions. 

The disk filter is similar to the dmm in operation, but filtration is conducted using a series of large diameter filter disks that carry the filter medium on both sides of the disk. They are connected to the main horizontal shaft and partly immersed in the feed slurry. The central shaft is connected by a set of valves which serve to provide vacuum and air as in dmm filters. As the disk sections submerge during rotation, vacuum is appHed to form a cake on both sides of the disk. The cycle of operation is similar to that in a dmm filter. One unit can have as many as 12 disks of up to 5-m diameter. Disk filters, both compact and cost effective, are used extensively in the iron ore industry to dewater magnetite concentrates. 

Duncan and Frankenthal report on the effect of pH on the corrosion rate of gold in sulphate solutions in terms of the polarization curves. It was found that the rate of anodic dissolution is independent of pH in such solutions and that the rate controlling mechanism for anodic film formation and oxygen evolution are the same. For the open circuit behaviour of ferric oxide films on a gold substrate in sodium chloride solutions containing low iron concentration it is found that the film oxide is readily transformed to a lower oxidation state with a Fe /Fe ratio corresponding to that of magnetite . 

Thus inhibitive anions can retard the dissolution of both the T-FejO, and the magnetite layers of the passivating oxide layer on iron. This has the dual effect of preventing breakdown of an existing oxide film and also of facilitating the formation of a passivating oxide film on an active iron surface, as discussed in the previous section. 

In October, 1910, the author had established the fact that certain magnetites as well as synthetic iron catalysts can be as effective as the uranium carbide catalyst which, in the hands of F. Haber, had proved to be of outstanding activity. At 500°C. and at a pressure of 100 atmospheres and a gas velocity of 50 liters per hour, 5 volume % of ammonia were obtained in the exit gases with 2 g. of a magnetite and 4.5% with a synthetic iron catalyst, the latter being operated at 550°C. 

The Mbssbauer effect involves resonant absorption of y-radiation by nuclei in solid iron oxides. Transitions between the I = Y2 the I = 72 nuclear energy levels induce resonant absorption (Fig. 7.4). A Mbssbauer spectrum is a plot of the transmission of the rays versus the velocity of their source movement of the source ( Co for iron compounds) ensures that the nuclear environments of the absorber and the source will match at certain velocities (i.e. energies) and hence absorption takes place. In the absence of a magnetite field the Mbssbauer spectrum consists of one (if the absorbing atoms are at a site of cubic symmetry) or two (symmetry distorted from cubic) absorption maxima. When a static magnetic field acts on the resonant nuclei, this splits the nuclear spin of the ground state into two and those of the ex-... 

Thermal decomposition of iron pentacarbonyl. Very finely divided red iron oxide is obtained by atomizing iron pentacarbonyl, Fe(CO)5, and burning it in excess of air. The size of the particles depends on the temperature (580-800 °C) and the residence time in the reactor. The smallest particles are transparent and consist of 2-line ferri-hydrite, whereas the larger, semi-transparent particles consist of hematite (see Chap. 19). The only byproduct of the reaction is carbon dioxide, hence, the process has no undesirable environmental side effects. Magnetite can be produced by the same process if it is carried out at 100-400 °C. Thermal decomposition of iron pentacarbonyl is also used to coat aluminium powder (in a fluidized bed) and also mica platelets with iron oxides to produce interference or nacreous pigments. 

In order to study the potential reducing capacity of some of the common accessory iron containing minerals measurements were performed with pyrite, magnetite, hornblende, biotite and chlorite in deaerated groundwater for Tc and U. Moreover, the effect of addition of a reducing agent (Fe2+) was investigated. 

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