Scientific publications

Forming of the chemical composition of groundwater is a most important geological problem. There is known empirical dependency the groundwater composition from time of water-rock contact. Aluminosilicate and carbonate rocks are wide-spread rocks on crystalline shield and have important role in enrichment of groundwater by chemical elements. Main purpose was to estimate the degree of the saturation of the solutions respect to a wide range of solid phases. The laboratory modeling of the water-rock interaction was organized. Some aqueous solutions were received in a result of quartzite (size <1 mm) leaching by distilled water in different conditions (various time of the water-rock interaction, various pCO2). Solutions were analyzed for physical-chemical parameters: conductivity, pH, Na, K, Ca, Mg, HCO3, Cl, SO4, Si, Al. The “fresh” rock contains the dissolved salts forming the alkaline solution of HCO3-Ca type with comparatively high Na, K, Cl concentrations. The repeated extractions from the same rock form the more diluting solutions. The CO2 saturation of water increases mineralization of solution and it type became whole HCO3-Ca.The saturation indexes were calculated using the software PHREEQC for a wide range of minerals using author's database of thermodynamic data (Parkhurst, 1999). The likelihood for a solid precipitating from an aqueous solution can be assessed by calculating the degree of saturation in the form of saturation index based on the activity of the individual ions in solution (Drever, 1997). The thermodynamic data and measured ions and parameters serve as input.
The calculation of the saturation index has shown that all solutions, even interacting with rock long time (43 days), in open system are unsaturated to all minerals except iron and aluminum oxides and hydroxides. In condition of CO2 saturation the solutions are supersaturated respect to secondary aluminosilicates even after 1 day of interacting. The results indicate that process of rock leaching is defined by thermodynamic disbalance of water with primary aluminosilicates, and CO2 is an important factor for change of balance conditions and forming of the chemical composition of groundwater.