Physical-chemical properties of complex natural fluids

Abstract

The dissertation is focused on the processes of transport and precipitation of metals in high temperature fumarole gases (a); thermodynamic properties of metamorphic fluids at high pressures (b); and the extent of hydrogen-bonding in supercritical water over wide range of densities and temperatures (c). (a) At about 10 Mpa, degassing of magmas is accompanied by formation of neary ‘dry’ salt melts as a second fluid phase, very strong fractionation of hydrolysis products between vapour and melts, as well as subvalence state of metals during transport processes. Based on chemical analyses of gases and condensates from high-temperature fumaroles of the Kudryavy volcano (i Iturup, Kuril Arc, Russia), a thermodynamic simulation of transport and deposition of oreand rock-forming elements in high-temperature volcanic gases within the temperature range of 373-1373 K at 1 bar pressure have been performed. The results of the numerical simulations are consistent with field observations. Alkali and alkali earth metals, Ga, In, Tl, Fe, Co, Ni, Cu, and Zn are mainly transported as chlorides in the gas phase. Sulfide and chloride forms are characteristic of Ge, Sn, Pb, and Bi at intermediate and low temperatures. Be, Al, and Si migrate as fluorides and oxides, while As and Sb as sulfides and oxides. More complex, oxyfluoride and oxychloride species are typical for Ti, Zr, V, Mo, W, and Re. Cd (at high temperatures) and Hg (within the whole temperature range) are transported in the native form. The calculations revealed some general regularities in the variation of element species in the gas phase at a low (1 bar) pressure and high temperatures. (b) Based on the thermodynamic perturbation theory, the equation of state (EOS) for the H-O-C-N-S-F-Cl-Br-I-B-Si-He-Ne-Ar-Kr fluid system has been developed. The EOS currently involves 98 different components and possess the following attractive features: 1) It is based on four substance specific parameters with clear physical meaning (dipole moment, polarizability and two parameters of the Lennard-Jones potential). 2) The EOS can be safely extrapolated to higher temperatures and pressures beyond the range of available P-V-T measurements. 3) The properties of fluid mixtures are determined from that of the pure fluid components. No additional parameters are involved. 4) New components can be easily added. The approach can be used as a basis for more general fluid systems involving strong electrolytes. (c) A series of Monte-Carlo and Molecular Dynamics simulations have been performed to study the extent of hydrogen-bonding in supercritical water over a wide range of temperatures and pressures. Depending on the P-T conditions, three different structural states of supercritical water were identified: 1) liquid-like structure dominated by the existence of the infinite percolating H-bonded network; 2) vapor-like structure dominated by separate lowmolecular (<10-20 molecules) clusters; and 3) intermediate type, where clusters of any size can be found in the bulk fluid. The stability field of the third structural type approximately corresponds to the density interval of 0.55-0.7 g/cm. Even at densities below 0.02 g/cm noticeable amounts of H-bonded clusters can be found in supercritical water. No significant density and temperature dependence of the relative abundance for topologically different water clusters of the small size was observed. The chain-like clusters were found to predominate under supercritical conditions over other possible cluster geometry.