Thermochemical Sulfate Reduction (TSR) by Methane - in Situ Observation and Raman Characterization in Fused Silica Capsules at Temperatures up to 450°C

Details Thermochemical Sulfate Reduction (TSR) by Methane - in Situ Observation and Raman Characterization in Fused Silica Capsules at Temperatures up to 450°C Thermochemical Sulfate Reduction (TSR) by Methane - in Situ Observation and Raman Characterization in Fused Silica Capsules at Temperatures up to 450°C

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p43b1402c&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P43B-1402

Other

1034 Hydrothermal Systems (0450, 3017, 3616, 4832, 8135, 8424), 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 3612 Reactions And Phase Equilibria (1012, 8412), 3665 Mineral Occurrences And Deposits, 5470 Surface Materials And Properties

Scientific paper

An experimental technique using optically transparent fused silica capsules has been developed for TSR studies. Reactions between sulfuric acid (5 m) and methane (~30 MPa) were observed and characterized by Raman spectroscopy at temperatures (T) up to 450°C. In situ Raman signals showed the transformation from sulfate (S6+) to sulfite (S4+), elemental sulfur (S0), and finally to sulfide (S2-) with the generation of CO2. The durations for each transformation range from a few minutes to a few tens of minutes depending on the T. The sample capsules were prepared by first loading sulfuric acid in a fused silica tube (0.3 mm OD, 0.1 mm ID, and ~6 cm long), which had one end sealed. The tube was attached to a vacuum line, methane was loaded cryogenically and the tube sealed with a hydrogen flame. (Chou et al., Geochim. Cosmochim. Acta, 2008, doi:10.1016/j.gca.2008.07.030). The sample was placed in a USGS-type heating-cooling stage and in situ Raman spectra were collected continuously during heating and cooling. In the aqueous phase (L), SO42- disappears at ~80°C and the transformation of HSO4- to SO2 in both aqueous and vapor (V) phases begins at ~350°C. Soon after L-V homogenization at ~410°C, CO2 was produced while HSO4- disappeared. Finally, SO2 transformed to S0, which was then reduced to H2S within 10 minutes. During cooling, L-V phase separation occurred at ~300°C (L-V homogenization T = 310°C), and only CO2, CH4, and H2S were detected in both L and V phases at room T. High concentrations of H2S in a number of deeply buried petroleum reservoirs (e.g., Orr, 1994, AAPG Bull., v. 50, p. 2295; Worden et al., 1995, AAPG Bull., v. 79, p. 854) are thought to be the product of TSR. However, reliable reaction kinetics as well as documented reaction mechanisms for TSR are still lacking. Our technique has great potential in examining TSR and also in the studies of ore forming processes in magmatic/hydrothermal (Rye, 2005, Chem. Geol., v. 215, p. 5) as well as Mississippi Valley type environments (Anderson, 1991, Econ. Geol., v. 86, p. 909).

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