The solubility of Sn(IV) oxide was determined in a dilute NaClO4
solution with pH 2 through 12 at ambient temperature. Both oversaturation
and undersaturation experiments were carried out in an inert gas glovebox
where the concentration of the oxygen and carbon dioxide were less than 1
ppm. The solubility of Sn(IV) oxide was 3×10-8 mol/1 at neutral
pH, and increased at pH >7.5. Equilibrium constants of soluble reactions
were calculated from the experimental data, using curve fitting method.The study suggests that the solubility of Sn(IV) oxide would be higher than
that provisionally used in current safety assessments of HLW disposal
sites.
Leaching of the iodide ion from BiPbO2I (BPI), BPI encapsulated in cement (BPIC) and AgI was studied in a low salinity solution and in a high salinity solution under reducing conditions. Although BPI released a limited amount of iodide ions (less than 1%) into the low salinity solution, it released more than 30% of iodide ions into the high salinity solution within 80 days. AgI released more than 30% of iodide ions into both low and high salinity solutions within 80 days. It was proved that BPI is more stable than AgI in the low salinity solution under reducing conditions. BPIC released a limited number of iodide ions (less than 5%) into both low and high salinity solutions. BPIC showed the best leach resistance in the high salinity solution.BiPbO2NO3 (BPN) was developed to remove iodide ions in a solution and fix them in BPI by the ion exchange reaction. Ion exchange properties under reducing conditions were studied. An anion exchange capacity of 1.0 mEq/g and a distribution coefficient of larger than 0.1 m3/kg were obtained in a solution at a pH of between 9 and 13. The advantages of the process using BPN for removing and immobilizing Iodine-129 were discussed from the standpoint of process simplification.
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