Other
Scientific paper
Oct 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992gecoa..56.3681d&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 56, Issue 10, pp.3681-3692
Other
11
Scientific paper
Experiments were performed to determine Fe-Cl speciation in aqueous fluids at temperatures from 200 to 450°C, pressures from 300 to 500 bars, and total dissolved Cl concentrations from 0.03 to 1.24 molal. The experiments made use of the assemblage hematite-magnetite to buffer key aspects of fluid chemistry. FeCl + and FeCl 2 0 species were found to best fit the experimental data. At relatively low temperatures (e.g., 200°C), our data agree with recent spectroscopic data, which show FeCl + to be the dominant form of dissolved Fe in low to moderate Cl-bearing aqueous fluids. At higher temperatures, however, FeCl 2 0 becomes increasingly significant. Taking explicit account of recent revisions to the HKF equation of state for aqueous species, we determined association constants for FeCl + and FeCl 2 0 as a function of temperature and pressure from measured pH, as well as dissolved Fe and Cl concentrations. At 300, 350, and 400°C, 500 bars, for example, log K (FeCl 2 0 ) values for the following reaction: Fe 2+ + 2 Cl - = FeCl 2 0 are 4.77 ± 0.05, 6.00 ± 0.07, and 7.51 ± 0.07, respectively. At 400°C, 400 and 300 bars, log K (FeCl 2 0 ) increases from 8.21 ± 0.12 to 10.89 ± 0.12. The results indicate the degree of association of FeCl 2 0 increases with increasing temperature and decreasing pressure. As conditions approach the supercritical region (NaCl fluid), the relative stability of the complex increases dramatically. Regression analysis of the association constant for FeCl 2 0 against the density of water results in the following relationship: log K (FeCl 2 0 ) = 16.042 (± 0.188) - 14.579 (± 0.311) d , where d is the density of water. This empirical relation can be applied to hydrothermal systems to constrain Fe mobility provided d falls within the range of 0.777 to 0.358 g/cm 3 . Fe-Cl complex data, along with our previously determined data for the effect of dissolved NaCl on activity coefficients of H 2( aq ) and H 2 S ( aq ) at elevated temperatures and pressures, permit us to constrain subseafloor hydrothermal alteration processes from dissolved Cl, Fe, H 2(aq) , and/or H 2 S (aq) concentrations of hot spring fluids. For example, assuming vent fluids at mid-ocean ridges equilibrate with pyrite-magnetite, subseafloor temperatures and pH ( in situ ) values of 372-394°C and 4.6-5.2, respectively, are indicated. These results are in good agreement with phase equilibria constraints involving plagioclase-epidote-quartz coexisting with Na-Ca-Cl fluids.
Ding Kaihe
Seyfried William E. Jr.
No associations
LandOfFree
Determination of Fe-Cl complexing in the low pressure supercritical region (NaCl fluid): Iron solubility constraints on pH of subseafloor hydrothermal fluids does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Determination of Fe-Cl complexing in the low pressure supercritical region (NaCl fluid): Iron solubility constraints on pH of subseafloor hydrothermal fluids, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Determination of Fe-Cl complexing in the low pressure supercritical region (NaCl fluid): Iron solubility constraints on pH of subseafloor hydrothermal fluids will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1869927