Of iron silicates

The first extensive study of iron-silicate minerals published was by deCoster and co-workers (7, 24). Their results are summarized in Table VI. Augite is a pyroxene containing considerable Na and Ca. No iron percentage was given for the olivine studies. The other minerals are included for comparison. The values given here for biotite are averages for their three untreated samples, which have two sites described as distorted octahedra. Heat treatment at 700°C. for one hour resulted in the emergence of a new Fe peak in biotite. 

Table VI. Mossbauer Parameters of Iron-Silicate Minerals Studied by deCoster, Poliak, and Amelinckx (7, 24) "...

Sulphate of eoda, Chloride of sodium Carbonate of soda, Hydrate of soda, Carbonate of lime, Oxysulphide of calcium SCaS + CaO], Sulphide of iron, Silicate of magnesia,. Charcoal, From Newe f tft.. ..23-57. , . 12-90. 34-76. . .. 4-74. . .. 2-02. From IftireAtila, Jildiurlsom. 25-64. 15-57., .. 1-22 4-28... 

A similar study of the reaction of acetylene with iron supported on quartz was made by Maksimov et al. (240). The Mossbauer spectrum before reaction with acetylene was a spectral doublet characteristic of iron silicate. After reaction at 1270 K for 50 sec the sample was quenched to room temperature, and in the subsequent Mossbaucr spectrum a new peak was noted. The intensity of this peak increased with increasing reaction time up to 0.1 hr, after which time the intensity remained constant. In this case, it was only possible to study the rate of this surface reaction using a series of low-temperature quenches, since the characteristic reaction time was the order of time required to obtain the Mossbauer spectrum. 

Figure 6. Hypothetical e vs. pH diagram showing how the presence of iron silicate may affect the stability relations in the Fe-Si-C02-H20 system...

Figure 8. Hypothetical e vs. pH diagram showing how the presence of various iron silicates may affect the stability relations in the Fe-S-Si-H20 system. The full lines refer to iron species, heavy dashed lines to the system H2S-HS"-SO/ Thin dashed lines indicate how the presence of iron silicates may decrease the highest pH at which iron sulfides are stable...

CSENCSITS GRONSKY Microstructural Study of Iron Silicate Catalyst 367... 

Figure 1--SEM image of iron silicate molecular sieve in the as-synthesized form, grown from an unstirred gel with Si02/Fe203-ratio 50, a-grown without alkali cations b-grown with added Li c-grown with Na cations and d-grown with K cations.

Diagenesis of iron silicate sediments in the absence of active forms of sulfur and carbon dioxide leads to some decrease in the silicate field due to expansion of the goethite field towards the region of reducing conditions (see Fig. 58). As in amorphous silicate sediments, the magnetite field in crystalline rocks is completely replaced by the greenalite field. 

Fig. 70. P-T curves of reactions of dehydration of iron silicates under conditions of low-temperature metamorphism.

Therefore the formation of magnetite in that way could hardly be of essential importance in the metamorphism of iron-formations, and martitiza-tion is still less hkely. However, in deposits of other genetic types, for instance skam deposits, oxidation of iron silicates to magnetite at the contact with large masses of carbonate rocks (dolomite, magnesite) can be considered an ore-forming process. The last conclusion is still feasible because the carbon dioxide released in the dissociation of carbonates probably had an undisturbed CO O2 ratio. 

Schott J. and Berner R. A. (1983) X-ray photoelectron studies of the mechanism of iron silicate dissolution during weathering. Geochim. Cosmochim. Acta 47, 2233 - 2240. 

The presence of iron in the weathering reactions is fundamental to lat-erite development and also derives from the breakdown of iron silicates. One of the simplest ferromagnesian mineral structures is that of fayalite (Fe-rich olivine), which is a common silicate in many mafic rocks according to Curtis (1976), ferric iron (Fe3+)may be produced directly from a simple oxidation and hydration reaction ... 

Schott, J. and R. A. Berner (1983), X-Ray Photoelectron Studies of the Mechanism of Iron Silicate Dissolution during Weathering, Geochim. Cosmochim. Acta 47, 2333-2340. 

XAFS studies of the crystal chemistry of iron silicate scale deposits in the Salton Sea geothermal field (Manceau et al. 1995)... 

For catalytic reduction processes, in which hydrocarbons were used as reducing agents, copper exchanged zeolites showed the best performance, for example for propene containing feed compositions [11], since close to 100% NO conversion could be attained at as low as 623 K. An acidic form of iron-silicate showed high activity and stability for reduction of NO with propene, but this catalyst was very sensitive to the presence of SO2 in the feed [12]. Metallosilicates having ZSM-5 structure [13,14] seem to be a new class of catalysts for these reactions. 

Catalyst Samples. Samples of the iron catalysts B-2 and B-6 provided by ERDA-PERC were produced from a mixture of magnetite and the appropriate oxides, by calcining the mixture in an open iron crucible for 15 min in an induction furnace to 1740-1775 K (8). The chemical analyses of the catalysts after calcining are shown in Table II. The most significant difference between the catalysts is the high Si02 content in B-2. Most likely, the formation of iron silicate contributed to the high Fe " /Fe in B-2 as compared to B-6. 

Figure 7.13. The coercive field of a granular film of iron silicate on a flat surface. It depends strongly on two-dimensional percolation of the particles. 

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