Calcium ground-water compositions

The content of Ca + in ground water is limited to the presence of carbonates and sulphates. At evaporation, calcium salts also are the first to precipitate. Nevertheless, it is the second in abrmdance among dissolved metals. In fresh water it often prevalent in concentrations over the others. With the increase in salinity its role in ground water composition grows, reaches some maximum and then is limited to carbonates and sulphates (3.10). However, at greater depths in the absence of CO " and SO " in brines calcium can have a very high concentration (up to 96 g-1 ). 

Most of the above diagenetic processes can occur in any of three environments. In the marine environment, the deposit is in contact with sea-water, which contains dissolved magnesium and may be either un-saturated, or super-saturated with respect to calcium carbonate species. In the ground-water environment, it is in contact with water, which is low in dissolved magnesium and is generally unsaturated with calcium carbonate. In the burial environment it is subject to high pressures and possibly elevated temperatures (or hydrothermal conditions) and is in contact with water, which may have a widely varying composition. 

That is exactly the competition between different forms of orientation interaction, which determines the composition and chemical properties of ground water. In very fresh water dominates orientation interaction between H O dipoles. As salinity and concentration of the dissociated ions, i.e., the simplest anions and cations (Na+, Ca +, Cl", COj ", etc.) grows, also increases the role of interaction between water and ions. At relatively high salinity ions have to interact between themselves, forming more complex associated ions (CaHCOj+, NaHCO ", HSiO ", HCO, etc.), capable of decomposing into simpler ones with freshening water. At this, the number of associated ions increases. Thus form complex super-molecular compounds with relatively weak bonds (PbClj, AlF, Fe OH ", etc.). Moreover, one and the same dissociated ion may be part of the composition of different associated ones. For instance, calcium in the sea water may exist simultaneously as Ca, [CaHCOj], [CaCOj, [CaSOj, etc. 

Chlorine in the earth crust is not very abimdant and it is highly dispersed. Small amounts of this element are in the composition of numerous minerals and rocks. However, main source are chlorides of alkali and alkali-earth metals, first of all halite NaCl. Rarer are potassium, calcium, magnesium chlorides bischofite, carnallite, sylvin, sylvinite, kainite and other evaporite or lake salt. The important source of chlorine in ground water is also sea water. 

The higher differences, in phase composition are observed in the pastes autoclaved in the saturated water vapour at temperature range 120-200 °C. The phase composition of the calcium sihcate hydrates is primarily the function of C/S in the starting mixture. In Portland cement paste without additions the C-S-H (I) is transformed quickly to the C-S-H (II) and the latter already at 25 °C into a-C2SH [194, 199]. The proper addition of the ground quartz gives the 1.1 nm tobermorite. This phase contains aluminium in solid solution, which causes the transition to xonotlite, at temperatures exceeding 160 °C difficult... 

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