Solid-solute phase equilibria in aqueous solutions X. Solubility constant and stability of norsethite

摘要

The solubility constant of norsethite, BaMg(CO3)(2), was determined for the first time. Also, a new method was developed which permits the precipitation of pure norsethite from homogeneous solution. The solubility measurements were performed at 25 degrees C in 0.20mol.dm(-3) sodium perchlorate media of constant ionic strength. It was shown that norsethite dissolves congruently in this solution. The pH variation method was used to obtain a stoichiometric solubility constant which was extrapolated to zero ionic strength by use of the Davies equation. The resulting thermodynamic solubility constant was incorporated in a comprehensive computer model which permits solubility calculations in complex systems. Thus, the conditions for norsethite formation in the environment and in the laboratory can be predicted. Furthermore, the stability of norsethite with respect to witherite (BaCO3) and the various magnesium carbonate phases was calculated. [References: 15]