Preliminary quantification of metal selenite solubility in aqueous solutions

Abstract

Selenium solubilization can be a potential source of environmental contamination in natural systems. Currently no experimental data are available on the solubility of metal selenites in aqueous solutions. The objective of our study was to determine the solubility of Ca, Mg, Mn, and Zn selenites. A dissolution study was conducted for 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35 and 40 weeks with CaSeO 3 · H 2O, MgSeO 3, MnSeO 3 and ZnSeO 3 · H 2O using different background solutions, including distilled deionized water (DI Water), 0.01 M NaCl, 0.03 M NaCl and 0.02 M Na 2SeO 3. For all solids, equilibrium was reached within 40 weeks. As compared to the theoretical values obtained from literature, the experimental p K 0 values for ZnSeO 3 · H 2O were higher, whereas for MgSeO 3 the determined p K 0 values were lower; theoretical and experimental data for both CaSeO 3 · H 2O and MnSeO 3 were comparable. A comparison of the p K 0 values also indicated that MgSeO 3 had the highest solubility in DI water, whereas in the three other solutions MnSeO 3 had the maximum solubility. The mean p K 0 values determined for CaSeO 3 · H 2O, MgSeO 3, MnSeO 3 and ZnSeO 3 · H 2O in the above mentioned background solutions were 7.76, 7.56, 7.11, and 7.70, respectively, which indicated that the overall solubility order would be, Mn SeO 3 > MgSeO 3 > ZnSeO 3 · H 2O > CaSeO 3 · H 2O. The results of this study are fundamental for modifying existing Se thermodynamic databases and understanding selenite solid-water interactions in natural environments.