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Abstract:
This chapter summarizes the equilibria of the chemical reactions occurring in CaCO3 - H2O - CO2 solutions, as they are typical for karst water. The evolution of the chemical composition of such solutions during their interaction with limestone depends on specific geological conditions, such as dissolution proceeding under the conditions of the open or closed system with respect to CO2. Since the CO2 concentration in karst water determines its further chemical evolution and the equilibrium concentration of Ca 2+ with respect to calcite in all cases of interest, equations are derived which describe the evolution of the chemical composition in the most general case, i.e. when a limited volume of gaseous CO2 is in contact with a solution dissolving limestone. This includes the cases of open and closed system with respect to CO2 as end members. Finally we discuss the influence of foreign ions common in karst, such as Mg 2+, SO4 2-, Na + and Cl - to the equilibrium concentration of dissolved Ca 2+ ions with respect to calcite.