H2S H2O Research Articles

Internally consistent data for sulphur‐bearing phases and application to the construction of pseudosections for mafic greenschist facies rocks in Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–CO2–O–S–H2O

AbstractThe Holland and Powell internally consistent data set version 5.5 has been augmented to include pyrite, troilite, trov (Fe0.875S), anhydrite, H2S, elemental S and S2 gas. Phase changes in troilite and pyrrhotite are modelled with a combination of multiple end‐members and a Landau tricritical model. Pyrrhotite is modelled as a solid solution between hypothetical end‐member troilite (trot) and Fe0.875S (trov); observed activity–composition relationships fit well to a symmetric formalism model with a value for wtrot−trov of −3.19 kJ mol−1. The hypothetical end‐member approach is required to compensate for iron distribution irregularities in compositions close to troilite. Mixing in fluids is described with the van Laar asymmetric formalism model with aij values for H2O–H2S, H2S–CH4 and H2S–CO2 of 6.5, 4.15 and 0.045 kJ mol−1 respectively. The derived data set is statistically acceptable and replicates the input data and data from experiments that were not included in the initial regression. The new data set is applied to the construction of pseudosections for the bulk composition of mafic greenschist facies rocks from the Golden Mile, Kalgoorlie, Western Australia. The sequence of mineral assemblages is replicated successfully, with observed assemblages predicted to be stable at X(CO2) increasing with increasing degree of hydrothermal alteration. Results are compatible with those of previous work. Assemblages are insensitive to the S bulk content at S contents of less than 1 wt%, which means that volatilization of S‐bearing fluids and sulphidation are unlikely to have had major effects on the stable mineral assemblage in less metasomatized rocks. The sequence of sulphide and oxide phases is predicted successfully and there is potential to use these phases qualitatively for geobarometry. Increases in X(CO2) stabilized, in turn, pyrite–magnetite, pyrite–hematite and anhydrite–pyrite. Magnetite–pyrrhotite is predicted at temperatures greater than 410 °C. The prediction of a variety of sulphide and oxide phases in a rock of fixed bulk composition as a function of changes in fluid composition and temperature is of particular interest because it has been proposed that such a variation in phase assemblage is produced by the infiltration of multiple fluids with contrasting redox state. The work presented here shows that this need not be the case.

Thermodynamic model for the phase equilibria of gases and brines. Example in the H2S-H2O-NaCl system

We present a thermodynamic model for the phase equilibria of gases and brines, which couples Henry's Law with the Soave–Redlich–Kwong equation of state to reproduce experimental data. In this communication we focus on the H2S H2O NaCl system.

Molecular simulation of the salting out effect in the system H2S–H2O–NaCl

The reduction of the solubility of a gas due to the presence of ionic species in a solvent is called "salting-out". The "salting-out" of hydrogen sulfide by sodium chloride in water was predicted by Gibbs ensemble Monte Carlo simulation at temperatures between 373 and 423 K and at salt molalities up to 10 mol kg(-1). The intermolecular interactions were modeled by combining Lennard-Jones potentials with Coulomb interactions. Several force fields were examined. The interactions between unlike species were estimated using two common combining rules without any adjustable parameters for the dispersion interaction. The simulations predict the "salting-out" of hydrogen sulfide by sodium chloride in aqueous solutions in an at least qualitative, partly in a quantitative manner.

Fluid chemistry and evolution of hydrothermal fluids in an Archaean transcrustal fault zone network: the case of the Cadillac Tectonic Zone, Abitibi greenstone belt, Canada

Detailed fluid geochemistry studies on hydrothermal quartz veins from the Rouyn-Noranda and Val-d'Or areas along the transcrustal Cadillac Tectonic Zone (CTZ) indicate that unmineralized (with respect to gold) sections of the CTZ contained a distinct CO2-dominated, H2S-poor hydrothermal fluid. In contrast, both gold mineralized sections of the CTZ (e.g., at Orenada #2) and associated higher order shear zones have a H2O–CO2 ± CH4–NaCl hydrothermal fluid. Their CO2/H2S ratios indicate H2S-rich compositions. The Br/Cl compositions in fluid inclusions trapped in these veins indicate that hydrothermal fluids have been equilibrated with the crust. Oxygen isotope ratios from hydrothermal quartz veins in the CTZ are consistently 2‰ more enriched than those of associated higher order shear zones, which are interpreted to be a function of greater fluid/rock ratios in the CTZ and lower fluid/rock ratios, and more efficient equilibration of the hydrothermal fluid with the wall rock, in higher order shear zones. An implication from this study is that the lower metal endowment of the transcrustal CTZ, when compared with the higher metal endowment in higher order shear zones (ratio of about 1 : 1000), may be the result of the lack of significant amounts of H2O–H2S rich fluids in most of the CTZ. In contrast, gold mineralization in the higher order shear zones appear to be controlled by the high H2S activity of the aqueous fluids, because gold was likely transported in a bisulfide complex and was deposited during sulfidation reactions in the wall rock and phase separation in the quartz veins.

Comparison of the sulfurization of CoMoK/Al2O3 catalyst with H2S and CS2

Only H2S consumption and H2O formation was found in the sulfurization of CoMoK/Al2O3 water gas shift catalyst with H2S/H2, but CO2 was formed first, then CH4, H2O and H2S appeared in the later part of TPS with CS2/H2. Carbon deposition on the catalyst during the sulfurization with CS2/H2 caused a lower activity than the catalyst sulfurized with H2S but could be removed in the run of WGS reaction.