Hydrothermal waters

Fig. 6. In a binary electricity generation plant, the hydrothermal water from the weU, A, is passed through a heat exchanger, B, where its thermal energy is transferred to a second, more volatile working fluid. The second fluid is vaporized and deflvered to a turbine, D. After exiting the turbine the spent working fluid is cooled and recondensed in another heat exchanger, E, using water or air as the coolant, F. It is then fed back to the primary heat exchanger to repeat the cycle. Waste hydrothermal fluid, C, can be reinjected into the producing field.

Kaolin most commonly originates by the alteration of feldspar or other aluminum siHcates via an intermediate solution phase (97,98) usuaHy by surface weathering (26,99) or by rising warm (hydrothermal) waters. A mica, or hydrated alumina soHd may form as an intermediate phase during the alteration from parent material to kaolin minerals. 

Reed, M.H. and Spycher, F. (1984) Calculation of pH and mineral equilibria in hydrothermal waters with application to geothermometer and studies of boiling and dilution. Geochim. Cosmochim. Acta, 46, 513-528. 

Albarede, F., Michard, A., Minster, J.F. and Michard, G. (1981) Sr/ Sr ratios in hydrothermal waters and deposits from the East Pacific Rise at 21°N. Earth Planet. Sci. Lett, 55, 229-236. 

Turekian, K.K., Cochran, J.K. and Krishnaswami, S. (1981) The flow rates of Galapagos spreading center hydrothermal waters determined with natural radionuclides. EOS, 62, 914. 

The decarboxylation of carboxylic acid in the presence of a nucleophile is a classical reaction known as the Hunsdiecker reaction. Such reactions can be carried out sometimes in aqueous conditions. Man-ganese(II) acetate catalyzed the reaction of a, 3-unsaturated aromatic carboxylic acids with NBS (1 and 2 equiv) in MeCN/water to afford haloalkenes and a-(dibromomethyl)benzenemethanols, respectively (Eq. 9.15).32 Decarboxylation of free carboxylic acids catalyzed by Pd/C under hydrothermal water (250° C/4 MPa) gave the corresponding hydrocarbons (Eq. 9.16).33 Under the hydrothermal conditions of deuterium oxide, decarbonylative deuteration was observed to give fully deuterated hydrocarbons from carboxylic acids or aldehydes. 

At lower temperatures, reducing conditions are present (CH4 is stable) this is typical for the oceanic crust. Most of the hydrothermal water circulates in the oceanic crust at a temperature of around 420 K, and the reducing conditions present there are mainly controlled by the PPM mineral mixture (Alt et al., 1989). 

Fig. 22.8. Energy yields for various anaerobic (top) and aerobic (bottom) metabolisms during mixing of a subsea hydrothermal fluid with seawater, expressed as a function of temperature, per kg of hydrothermal water. Energy yields for acetoclastic methanogenesis and acetotrophic sulfate reduction under oxic conditions are hypothetical, since microbes from these functional groups are strict anaerobes and cannot live in the presence of dioxygen.

Volcanic gases and associated hydrothermal waters have a large range in 8 C1-values from —2 to +12%o (Bames et al. 2006). To evaluate chlorine isotope fractionations in volcanic systems, HCl liquid-vapor experiments performed by Sharp (2006) yield large isotope fractionations of dilute HCl at 100°C. These results are in contrast to liquid-vapor experiments by Liebscher et al. (2006) observing very little fractionation at 400 - 450° C. Clearly more data are needed to resolve these discrepancies. 

Macdonald, D.D., Greidanus, J.W., Hyne, J.B., Hydrothermal (Water) Reactions of Athabasca Bitumen Organosulphur Model Compounds and Asphaltene , The Oil Sands of Canada-Venezuela 1977, CIM Special Volume 17. 

A 2-line ferrihydrite deposit is also formed from hydrothermal fluids at 60-93 °C upon mixing with sea water near the coast of Amberlite Island, Papua New Guinea. The hydrothermal waters are rich in As which is almost completely captured by the ferrihydrite (50-60 g As/kg), thereby hindering the formation of better crystalline Fe oxides and also preventing any toxic effects on the marine biota (Pichler, et al. 1999 Pichler and Veizer, 1999 Rancourt et al. 2001). Spherical, lOnm-sized, Si-containing,... 

J. Am. Ceram. Soc. 82 1937-1940 Konhauser, K.O. Ferris, F.G. (1996) Diversity of iron and silica predpitation by microbial mats in hydrothermal waters, Iceland Implications for Precambrian iron formations. 

The nature of oxygen transport within minerals in the presence of hydrothermal water and the role of diffusion. Chem. Geol. 53, 197-206. 

Fig. 5. In a double-flash plant for producing electricity from hydrothermal water, superheated water is delivered from the well, A, to an initial flashing unit, B, where the pressure is reduced to release steam which drives a turbine, D. The liquid fraction is then delivered to a second flashing unit, C, where further pressure reduction produces more steam which is introduced to the turbine at an intermediate stage. The waste fluid from the second flashing stage, E, may contain very high concentrations of dissolved or suspended solids, presenting significant disposal problems. The spent steam can be recondensed and...

Kaolin most commonly originates by the alteration ol feldspar or other aluminum silicates via an intermediate solution phase, usually by surface weathering or by rising warm (hydrothermal) waters. 

Like pH and pA"Sp, any dissociation constant may be conveniently written as a p/fa value, where p/fa = —log10 A a. That is, the p/fa of Reaction 2.41 at 25 °C and 1 bar pressure is about 9.2 (Table 2.10). Furthermore, like pH, p/fa values are often sensitive to temperature. In hydrothermal waters, for example, the pA a value of Reaction 2.43 declines with increasing temperature so that the value approaches 7.11 at 300 °C (Zakaznova-Herzog, Seward and Suleimenov, 2006), 1936 Table 2.10. 

Under anoxic conditions in the subsurface, precipitation/coprecipitation, sorption, and dissolution reactions in hydrothermal fluids commonly involve realgar (AsS or AS4S4), arsenopyrite (FeAsS), arsenian pyrite (FeS2), and especially orpiment (AS2S3). Orpiment dissolves in reducing and low H2S hydrothermal waters at temperatures up to at least 300 °C as shown in the following reaction (Webster and Nordstrom, 2003, 110) ... 

As(III) chloride complexes could exist in some highly acidic and saline fluids. However, in most hydrothermal waters, chloride and inorganic arsenic would not form complexes (Ballantyne and Moore, 1988, 475-476, 478). 

Once hydrothermal fluids approach the surface, lower pressures cause the liquids to boil. As steam separates from hydrothermal water, arsenic preferentially remains in the liquid phase. Above 200 °C, only about 0.1-0.5% of the arsenic in surface and near-surface hot springs partitions into steam (Ballantyne and Moore, 1988, 477). Table 3.6 lists the arsenic concentrations in condensates of gases from various volcanoes and hot springs. 

Geothermal water If hydrothermal waters reach the Earth s surface as hot springs and geysers, they are identified as geothermal waters. Geothermal waters may also have economic benefits, such as generating electricity, promoting tourism, and utilization in spas. 

Groundwater Subsurface water in the saturated zone. If the groundwater is above 50 °C, it is usually classified as hydrothermal water. 

Hydrothermal Water heated by the Earth to more than 50 °C. 

Figure 4.6 Large excesses of juvenile He in hydrothermal waters sampled at specific vent fields in the Galapagos Rift. Note ambient sea water concentration near origin (cf. Table 4.6). Reproduced from Jenkins et al. (1978).

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