An experimental study of Na, Mn, Sr and Ba partitioning between dolomite and MgCl₂ solution at 130 and 200°C

Abstract

The apparent partition coefficients (D_Me) of Na, Mn, Sr and Ba (Me) between dolomite and MgCl₂ solutions at 130 and 200°C, D_Me = (X_Me/X_Ca+Mg)_dolomite/([Me]/[Ca+Mg])_solution, were experimentally investigated, and the obtained average values were 0.0016, 5.3, 0.059 and 0.021, respectively. The Na partition coefficient was smaller than those of the above divalent ions, reflecting the valence discrepancy between Ca and Na. The partition coefficients of divalent ions decreased from Mn to Ba, which is consistent with the effect of the cation site size in the crystal lattice and the ionic radii of substituting elements. Comparing these solid/liquid partition coefficients for dolomite with those for calcite and aragonite seen in the literature, the former values resemble those for calcite, but are rather different from those for aragonite. These findings may reflect the sizes of the respective cation sites, since the cations in calcite and dolomite occupy relatively compact six-fold coordination sites, but aragonite has relatively large nine-fold sites.