Pyrite Mossbauer spectra

Figure 7. Mossbauer spectrum of a Waynesburg coal (RT). Szomolnokite, illite, and pyrite are identifiable.

Neutron capture in-beam Mossbauer spectrum of FeS2 (pyrite type) at room temperature. Measurement time was 70 h. (Reproduced from Ref. 66 with permission of Springer.)... 

Mossbauer spectrum after exposure time of 8 days (pyrite doublet just visible). 

Mossbauer spectrum of the coal from the Landau mine containing 3% pyrite. 

After the HT-XRD experiments were conducted, a Mossbauer spectrum for each sample was obtained. The resulting Mossbauer spectrum yielded Fe-containing glass and hematite as shown in Fig. 30.12. The possible occurrence of the intermediate pyrrhotite phase, due to the decomposition of pyrite, was not observed. 

A word of caution concerning the presence of trivalent sulfates in the coal is appropriate here. These sulfates have, in general, lines that overlap with the Mossbauer pyrite lines. The result is the detection of a slightly asymmetric pyrite spectrum. If one treats the samples with HCl, it will appear as if some of the pyrite had dissolved in HCl, but this observation, of course, is not true the observation results from the presence of the iron sulfates. The ferric sulfates are easily distinguishable from pyrite. When Mossbauer measurements are carried out at 4.2 K in the presence of a large external field, the characteristic hyperfine field of Fe " " is detected (about 500 kOe). It was observed also that many of the ferric sulfates are formed during LTA experiments (3). 

Figure 3. Room temperature Mossbauer spectra of coal samples from the Pratt seam in Alabama (top) and from an anthracite deposit in Rhode Island (bottom). In the top spectrum, peaks indicated arise from iron in the common coal minerals pyrite (P), clays (C), siderite (S), and jarosite (J), In the bottom spectrum, peaks indicated arise from iron in clays (C), and in the rare coal minerals, ankerite (A), iron metal (I), and ferric oxide (H),...

Fine coal samples were pressed into briquettes to simulate the compacting occurring during transportation and it was found that the amount of water contained in the coal declined by a factor of about 2 as compaction pressures increased from an initial pressure of 51 to a final pressure of 251. The amount of water in the samples compacted at 51 was 8.3% for the coal containing 3% pyrite and 11.9% for the coal containing only 0.6% pyrite. The briquettes pressed at a 51 compaction pressure were then placed on cleaned steel coupons for predetermined times and CEMS mode Mossbauer spectroscopy was conducted on the steel samples with the resulting spectrum presented in Fig. 30.11. 

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