PRELIMINARY QUANTIFICATION OF METAL SELENITE SOLUBILITY IN AQUEOUS-SOLUTIONS

Selenium solubilization can be a potential source of environmental con tamination in natural systems. Currently no experimental data are avai lable on the solubility of metal selenites in aqueous solutions. The o bjective of our study was to determine the solubility of Ca, Mg, Mn, a nd Zn selenites. A dissolution study was conducted for 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35 and 40 weeks with CaSeO3 . H2O, MgSeO3, MnSeO3 and ZnSeO3 . H2O using different background solutions, including disti lled deionized water (DI Water), 0.01 M NaCl, 0.03 M NaCl and 0.02 M N a2SeO3. For all solids, equilibrium was reached within 40 weeks. As co mpared to the theoretical values obtained from literature, the experim ental pK(0) values for ZnSeO3 . H2O were higher, whereas for MgSeO3 th e determined pK(0) Values were lower; theoretical and experimental dat a for both CaSeO3 . H2O and MnSeO3 were comparable. A comparison of th e pK(0) values also indicated that MgSeO, had the highest solubility i n DI water, whereas in the three other solutions MnSeO, had the maximu m solubility. The mean pK(0) values determined for CaSeO3 . H2O, MgSeO 3, MnSeO3 and ZnSeO3 . H2O in the above mentioned background solutions were 7.76, 7.56, 7.11, and 7.70, respectively, which indicated that t he overall solubility order would be, MnSeO3 > MgSeO3 > ZnSeO3 . H2O > CaSeO3 . H2O. The results of this study are fundamental for modifying existing Se thermodynamic databases and understanding selenite solid- water interactions in natural environments.