Vapor-liquid Ratios Research Articles

Fractionation of cadmium isotope caused by vapour-liquid partitioning in hydrothermal ore-forming system: A case study of the Zhaxikang Sb–Pb–Zn–Ag deposit in Southern Tibet

Here, we conducted a case study of the Zhaxikang Sb–Pb–Zn–Ag deposit to explore Cd isotopic fractionation mechanisms in hydrothermal ore-forming system. The δ114/110Cd values of sphalerite systematically decrease from ore mineralization stage 1 (−0.30‰ to 1.01‰; average value = 0.17‰; n = 4) through stage 2 (−0.51‰ to −0.09‰; average value = −0.23‰; n = 3) to stage 3 (−0.34‰ to −0.23‰; average value = −0.285‰; n = 2). A simple Rayleigh distillation models this temporally decreasing trend resulted from Cd isotopic fractionation that is most likely related to vapor-liquid dynamics of ore-forming fluid. This mechanism for Cd isotopic fractionation is further augmented by the general geochemical characteristics and fluid inclusion data of sulfides and cogenetic gangue minerals. Firstly, the sphalerite has low Cd concentrations (1183–2199 ppm), correspondingly high Zn/Cd ratios (248–421), and large Cd isotopic variation range with relatively lower δ114/110Cd values (−0.51‰ to 1.01‰). Commonly, sphalerite from sedimentary exhalative systems possess these characteristics caused by vapor-liquid interactions. Secondly, fluid inclusion data from the Pb–Zn sulfides and cogenetic carbonate alteration minerals indicates that vapor-liquid two-phase inclusions are in dominance (more than 90%). Meanwhile, the vapor-liquid ratios (20–50%) of these two-phase inclusions are consistent with those of the established Cd (25.48–55.07%) and Zn (26.70–48.70%) isotopic Rayleigh distillation model. To conclude, vapor-liquid partitioning is main cause for observed Cd isotopic variations in Zhaxikang deposit, and is demonstrated as an important Cd isotopic fractionation mechanism in hydrothermal ore-forming system.

Simulation of volatility of commercial gasoline based on major hydrocarbon species

Fuel volatility affects evaporative emissions and driveability. It is the property that must be changed with location and season. As exhaust gas emissions regulations become stringent, the margin of fuel injection schedule to allow for the variations of fuel volatility needs to be controlled tightly. It requires better understanding of fuel volatility effects on exhaust gas emissions and driveavility. Therefore, the modeling of fuel volatility is an essential basis for all theoretical approaches to address these issues. For the modeling, commercial gasolines were simplified with 13 major hydrocarbon species based on the carbon number and hydrocarbon families. Thermodynamic states of modeled fuels were calculated by the program SUPERTRAPP released by NIST (National Institute of Science and Technology). The program is based on the Peng-Robinson equation of state. The compositions of simulated fuels were calibrated with the specifications of commercial gasolnes such as ASTM distillation curve. Comparison with real fuels shows good agreement in front-end volatility represented by Reid vapor pressure and vapor-liquid ratios.

Geothermal gas equilibria

Comparison of theoretical and analytical equilibrium constants based on the reactions CH 4 + 2 H 2 O = CO 2 + 4 H 2, 2 NH 3 = N 2 + 3 H 2 and iron(II)-aluminium-silicate + 2H 2S = FeS 2 + H 2 + aluminium-silicate, shows that the composition of fluids discharged from geothermal areas in New Zealand (Wairakei, Kawerau, Broadlands) reflects close to complete attainment of chemical equilibrium within the system H 2O, CO 2, H 2S, NH 3, H 2, N 2 and CH 4. Under conditions prevailing in explored geothermal systems in New Zealand, the minerals graphite (elemental carbon), anhydrite, pyrrhotite, magnetite do not appear to take part in the overall equilibrium system. The three physical parameters required to evaluate geothermal gas reactions are temperature, pressure and vapor-liquid ratios within the gas equilibration zone.