Transport of Relevant Components
For the smart Kd-concept, the transport of Ca, DIC, Al, SiO4, and protons (and hydroxyl ions) is considered in the flow and transport code d3f++. Since Calcite (CaCO3 – Cc) is the sink/source for Ca and DIC it needs to be balanced. Furthermore, it is assumed that the concentration of free calcium ions [Ca2+] equals the total concentration of calcium [Ca]tot. In the considered pH range between 3 and 9, the contribution of further solution species as Ca(HCO3)+, CaCO30 und Ca(OH)+ is always below 2 % and therefore neglected here. The initial concentrations of Ca and DIC as well as the initial pH-value are usually derived from equilibrium calculations. Since the pH-value, and the activities of Ca, DIC, Al, and SO4 are a function of the ionic strength (IS), an activity correction is required, for which currently the SIT approach is used (Bulk solution activity correction).
The concept including all equations is described in the WEIMAR final report by HZDR and GRS.