Fe2+/Fe3+ ratio

Mossbauer spectroscopy may be used for semi-quantitative or qualitative determination of Fe2 /Fe3 ratios Table II shows that a rather good correlation exists between Mossbauer and chemical analysis for Fe2 /Fe3 ratios in clay mineral samples, but these measurements must be obtained at lower temperatures (< 150 K) in order to maximize the recoil-free fractions of both valence states in the sample ... 

Initially the solution is mostly Fe2+. As Ce4+ is added, the iron is oxidized and the potential slowly rises as the Fe2+/Fe3+ ratio decreases,... 

In most ores, sufficient Fe is already present. For some ores, it is necessary to add metallic iron. In practice, the oxidation potential of the solution can be monitored and controlled using the Fe2+/Fe3+ ratio. Very high leaching efficiencies with H2S04 are common, eg, 95—98% dissolution yield of uranium (39). If acid consumption exceeds 68 kg/1 of ore treated, alkaline leaching is preferred. The comparative costs of acid, sodium hydroxide, and sodium carbonate differ widely in different areas and are the determining factor. 

The treatment of sodium-bentonite with acetone causes no significant changes in the Mossbauer spectrum. The Fe2+ Fe3+ ratio practically remains approximately the same. It is in agreement with the results of x-ray diffraction studies showing no change in the lattice parameters. 

Table 5 gives the results of partitioning tests with both the M(IV) and M(VI) combinations. For the M(VI) case, 0.06M and 0.08M FeSA are -80% and 105%, respectively, of the stoichiometric amount of reductant necessary to completely reduce Np and Pu. The higher Pu loss might be caused by too low a Fe2+/Fe3+ ratio in the scrub section of the mixer-settler. When enriched U solutions were processed, Fe2+/Fe3+ ratios less than 0.18 led to oxidation of Pu(III) and Np(IV) (L3). The Fe2+/Fe3 + ratio of 0.054 in the scrub section would allow oxidation and re-extraction of Pu. Np loss is not changed because most of the Np does not reach the scrub section. Rather than increase waste... 

Chemical analysis Chemical analyses on suspension or powder samples were performed by a volumetric method (0.05 normal potassium dichromate) following dissolution in hydrochloric acid. The ferrous (Fe2+) content was determined directly. The ferric (Fe3+) content was analyzed via the Zimmermann-Reinhardt (SnCl2 reduction) technique, which gives the total iron. Subtraction of the Fe2+ gives the desired Fe3+ value. The Fe2+/Fe3+ ratio was determined with an accuracy of 0.01. The accuracy of the determination of the total iron was 0.5% of the result. Chloride content was determined by Volhard titration with an accuracy of 5% of the result. Nitrogen content was analyzed with the Nessler method with a relative accuracy of 15%. 

Added substrates changed the stoichiometry to < 2 1. The decrease is caused by both lack of formation of the full equivalent of [Fe /jq 1 because of the competition in Eq. (12), and partial reduction of already formed Fe3+ by the reducing radicals, Eq. (13). From the effect of [substrate] on the yields of Fe2+, the ratio of rate constants kpjkx was obtained. These ratios were then used to calculate the relative rate... 

The calculations described above allow us to plot the titration curve for Reaction 16-1 in Figure 16-2, which shows potential as a function of the volume of added titrant. The equivalence point is marked by a steep rise in voltage. The value of E+ at Ve is the formal potential of the Fe3+ Fe2+ couple, because the quotient [Fe2+]/[Fe3+] is unity at this point. The voltage at any point in this titration depends only on the ratio of reactants their concentrations do not figure in any calculations in this example. We expect, therefore, that the curve in Figure 16-2 will be independent of dilution. We should observe the same curve if both reactants were diluted by a factor of 10. 

There is a change in the ratio of the concentration Fe2+/Fe3+ and Ru2+/Ru3+ with consequent alteration in the redox potentials and hence a small change in the emf of cell. If the oxidation of Ru2+ to Ru3+ and reduction of Fe3+ to Fe2+ are made to occur at two electrodes current will flow in the external circuit. 

A second pathway involves the formation of a mixed-valent [Fe2+, Fe3+]-superoxo species that could react with a second molecule of 36 to form a peroxo-bridged tetranuclear [Fe +, Fe2+] cluster. Homolytic cleavage of the peroxo 0-0 bond followed by electron transfer and rearrangement would yield 37. These two pathways differ in their oxygen stoichiometry pathway 1 has a ratio of 02/reduced iron dimer of 1 1, whereas pathway 2 has a ratio of 1 2. Manometric measurements of 02... 

The influence of the Fe2+/Fe3+ molar ratio on the characteristics of magnetite particles obtained by co-precipitation of Fe2+ and Fe3+ (composition, size, morphology and magnetic properties) was studied by Jolivet (Jolivet et al., 1992). Chemical sp>ecies in different proportions were precipitated with ammonia solution to pH ll. The analysis of the products obtained with different Fe2+/Fe3+ molar ratios, in the range 0.10-0.50, concluded that for values lower than 0.30 two different phases coexist ... 

The influence of ionic species concentrations on the properties of magnetite particles was also followed. It was noted that the Fe2+/Fe3+ molar ratio was a determining factor in obtaining sub-micron sizes, while by increasing the ratio, the mean diameter of the magnetic particles increased, but unfortunately the yield decreased (Babes et al., 1999). 

Sample Dopant Doping number (atomic ratio) Fe2+ /Fe3+ Crystal phase Defect concentration (x) of Fe2+ in Fei xO... 

Fig. 3.37 Relationship between the ratio of various surface areas to the total surface area and Fe2+/Fe3+...

Sample No. Fe2+/Fe3+ Phase composition (By XRD) Main phase Minor phase Abrasion ratio/wt%... 

During the addition of the cerium(IV) solution up to the equivalence point, its only effect will be to oxidise the iron(II) (since K is large) and consequently change the ratio [Fe3+]/[Fe2 + ], When lOmL of the oxidising agent have been added, [Fe3+]/[Fe2 + ] = 10/90 (approx.) and... 

Silicates having an O Si ratio larger than or equal to 4 are orthosilicates, i.e. the Si04 tetrahedra do not share atoms with each other, but with the polyhedra about the other cations. Examples olivines, M2Si04 (M = Mg2+, Fe2+) and garnets, M3M2[Si04]3 (M = Mg2+, Ca2+, Fe2+ M = Al3+, Y3+, Cr3+, Fe3+). 

Gas emission after core formation the redox state in the iron-containing minerals of the Earth s crust is determined by the ratio of Fe2+ to Fe3+. 

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