The influence of La3+ on calcite formation was studied using CaCl2-NaHCO3 solutions. We adopted a closed system, where the pH change of the solutions was monitored in a closed vessel. The closed system reduces a number of thermodynamic variables of the solution, thus enabling us to calculate the amount of CaCO3 precipitate only from pH with the assumption of equilibria among dissolved components in solution. After the analytical inspection of the calculation and assumption on which the calculation is based on, it was applied to experiments of the calcite formation in a Teflon vessel. The mole concentration of lanthanum added in the experiments was smaller than 1/3000 of that of calcium ion in the solutions. The addition of lanthanum oxide, chloride, and nitrate caused the difference in the pH change of the solution. The decrease of pH was smaller when lanthanum reagents were added, indicating that the amount of CaCO3 precipitate decreased. The smallest decrease was observed when lanthanum chloride or nitrate salt was added. The X-ray diffraction study showed that the CaCO3 precipitated in any solutions were calcite. If an equilibrium is assumed, which is considered to be likely from the pH change, the ion activity product (IAP) calculated in this study increased about 6 times when lanthanum ion, whose concentration is only 1/14 000 mole of calcium ion, was present.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology