Chloride saturated with calcium sulfite

Figure 4. Dissolved sulfite concentration as a function of magnesium concentration and chloride-to-magnesium ratio for liquors saturated with calcium sulfite and gypsum at pH 5.5 and 50°C...

Precipitation of Carbonate Salts. In the Appendix, equations are given for the calculated degrees of saturation of calcite, S3, and of dolomite, S4, based on regression of these properties at the conditions shown in Table III. Figure 7 shows the effects of pH and PCo2 for solutions that are saturated with calcite or dolomite. In each case the solutions are saturated with calcium sulfite and gypsum, and the content of sodium chloride is 200 mmoles/kg H20. 

For liquors saturated with both calcium sulfite and gypsum, the concentration of dissolved sulfite species increases linearly with dissolved magnesium concentration, decreases linearly with dissolved chloride concentration, and is only weakly affected by pH. 

Dissolved Concentrations of Calcium and SO2 Species. The equilibrium dissolved concentrations of total calcium and SO2 (sulfite plus bisulfite) species are important because comparison of these equilibrium concentrations with actual measured values determines the degree of gypsum saturation, and hence the potential for gypsum scale formation in the scrubber. As a first approximation, the fraction gypsum saturation of a scrubber liquor, having specified pH and specified concentrations of magnesium and chloride, is proportional to the measured calcium concentration, and inversely proportional to the measured S02 concentration. 

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