Distribution coefficient of Mg 2+ ions between calcite and solution at 10–50°C

Abstract

The distribution coefficient ( λ Mg) of Mg 2+ ions between calcite and solution was found to be 0.012 ± 0.001 (10°C), 0.014 ± 0.001 (15°C), 0.019 ± 0.001 (25°C), 0.024 ± 0.001 (30°C), 0.027 ± 0.001 (35°C) and 0.040 + 0.003 (50°C). This indicates a remarkable dependence on temperature. The effect of the Mg 2+/Ca 2+ molar ratio in a parent solution on λ Mg for calcite is small, where the molar ratio lies in the range 0.04-2. However, the λ Mg value for aragonite tends to decrease with increasing Mg 2+/Ca 2+ ratio in the parent solution. The largest Mg content of calcite in the Ca(HCO 3) 2-Mg 2+ → calcite system is around 2 mol% in the temperature range 10–50°C. Neither homogeneous nor heterogeneous distribution laws hold for aragonite precipitation, and the temperature effect on the coprecipitation of Mg 2+ ions with aragonite is very small.