SOLID-SOLUTE PHASE-EQUILIBRIA IN AQUEOUS-SOLUTIONS X - SOLUBILITY CONSTANT AND STABILITY OF NORSETHITE

The solubility constant of norsethite, BaMg(CO3)(2), was determined fo r the first time. Also, a new method was developed which permits the p recipitation of pure norsethite from homogeneous solution. The solubil ity measurements were performed at 25 degrees C in 0.20mol.dm(-3) sodi um perchlorate media of constant ionic strength. It was shown that nor sethite dissolves congruently in this solution. The pH variation metho d was used to obtain a stoichiometric solubility constant which was ex trapolated to zero ionic strength by use of the Davies equation. The r esulting thermodynamic solubility constant was incorporated in a compr ehensive computer model which permits solubility calculations in compl ex systems. Thus, the conditions for norsethite formation in the envir onment and in the laboratory can be predicted. Furthermore, the stabil ity of norsethite with respect to witherite (BaCO3) and the various ma gnesium carbonate phases was calculated.