The source of sodium in groundwater, Pannonian Basin, Hungary

One of the main sources of sodium in the subsurface waters of the study region is feldspar weathering. Standard formation Gibbs energy and standard enthalpy of albite weathering into montmorillonite were calculated based on the method developed by Tardy & Garrels (1974). Ion activity product of the reaction was also calculated in the subsurface waters of the 100-2500 in depth interval. Temperature dependence of the equilibrium constant and that of the LAP values indicate that the driving force of the reaction is effective up to 70-80 degreesC.