Influence of anion background on transport of calcium and magnesium

Anions in solution may affect cation exchange on the solid matrix by forming complexes. The importance of this effect for transport depends on the charge and stability of the complexes formed. Studies indicate that this effect might be important for cation complexes with anions. In this study batch and column experiments were performed in order to compare the influence of chloride, perchlorate, and sulfate on transport and equilibrium ion exchange of calcium and magnesium in two forest soils. The batch experiments indicated that the selectivity coefficient for Ca vs. Mg is lower in a perchlorate or sulfate than in a chloride background. The anion background was not found to influence Mg-Ca breakthrough curves. However, differences of estimated parameters between runs with the same anion were large and exceeded those between runs with different anions.