ABSTRACT

The present authors have studied the influence of barium and magnesium ions, which are contained together in a calcium bicarbonate parent solution, on the crystal form of carbonate formed from the parent solution. Magnesium ions in a parent solution inhibit calcite formation and favor aragonite formation, whereas barium ions inhibit aragonite formation and favor calcite formation. The degree of these influences is affected by the concentrations of these ions in the parent solution. When the influence of barium ions is stronger than that of magnesium ions, magnesian calcite is formed and the MgCO₃ content of the magnesian calcite increases with increasing concentration of magnesium ions in a parent solution. From the calcium bicarbonate solutions containing both more than 35ppm of barium ions and 1, 200ppm of magnesium ions monohydrocalcite is formed. Monohydrocalcite does not incorporate both MgCO₃ and BaCO₃ in its crystal lattice. The distribution coefficients of magnesium and barium have been measured when magnesian calcite is precipitated. The distribution coefficient of magnesium or barium for magnesian calcite tends to increase with increasing barium carbonate content or magnesium carbonate content of the formed magnesian calcite, respectively.