Effects of Aging Quartz Sand and Hanford Site Sediment with Sodium Hydroxide on Radionuclide Sorption Coefficients and Sediment Physical and Hydrologic Properties: Final Report for Subtask 2a

Abstract

Column and batch experiments were conducted in fiscal year 1998 at Pacific Northwest National Laboratory' to evaluate the effect of varying concentrations of NaOH on the sorptive, physical, and hydraulic properties of two media: a quartz sand and a composite subsurface sediment from the 200-East Area of the Hanford Site. The NaOH solutions were used as a simplified effluent from a low-activity glass waste form. These experiments were conducted over a limited (0-to 10-month) contact time, with respect to the 10,000-to 100,000-year scenarios described in the Immobilized Low-Activity Waste-Performance Assessment (ILAW-PA).Whe? these two solids were put in contact with the NaOH solutions, dissolution was evident by a substantial increase in dissolved Si concentrations in the leachates. Incremental increases in NaOH concentrations, resulted in corresponding increases in Si concentrations. A number of physical and hydraulic properties also changed as the NaOH concentrations were changed.It was observed that quartz sand was less reactive than the composite sediment. Further, moistureretention measurements were made on the quartz sand and composite sediment, which showed that the NaOH-treated solids retained more water than the non-NaOH-treated solids. Because the other chemical, physical, and hydraulic measurements did not change dramatically after the high-NaOH treatments, the greater moisture retention of the high-NaOH treatments was attributed to a "salt effect" and not to the formation of small particles during the dissolution (weathering).The distribution coefficients (Kds) for Cs and Sr were measured on the NaOH-treated sediments, with decreases from -3,000 to 1,000 and 1,300 to 300 mL/g noted, respectively, at the 0.01-to 1.0-M NaOH levels. There was no apparent trend for the Sr I<d values with contact time. The lack of such a trend suggests that dissolution of sediment particles is not controlling the drop in &; rather, it is the competition of the added Na in the various treatment solutions.It is clear from these experiments that the background chemistry of the waste-glass leachate is likely to have a significant effect on the hydrology and radionuclide geochemistry in the near-field environment of the ILAW. These experiments provided an important first approximation of several chemical and physical processes. Future research, together

Sorption of europium(III) on polymeric silica in perchlorate media

“…The coagulation process is favored by the increase in ionic strength and silica concentration. The presence of CO 3 2− has negligible effect on the sorption of Eu(III) ions in pH range 7.0 to 9.0. Binding capacity of the metal ions follows the order of their ionic potential, i.e., M 3+ > M 2+ > M + ; and the critical coagulation concentration follows the order: M 3+ < M 2+ < M + .…”

“…Fig. 4 shows that under our experimental conditions, the presence of 1.00 × 10 −3 M CO 3 2− ions has a marginal effect on the sorption of Eu(III) ions. This is likely due to the complexing effect of the higher concentration of polymeric silica compared to that of the CO 3 2− [18,31].…”

“…The solution chemistry of radionuclides in natural waters is influenced by their hydrolytic behavior and by reactions with different natural ligands such as CO 3 2− , HCO 3 − , F − , Cl − , SO 4 2− and silicate. The interaction of CO 3 2− ions with the cationic radionuclides is very important in view of its relatively wide range of concentration (50-860 mg/L) in ground waters of different waste disposal sites [30].…”

“…The interaction of CO 3 2− ions with the cationic radionuclides is very important in view of its relatively wide range of concentration (50-860 mg/L) in ground waters of different waste disposal sites [30]. Therefore, the sorption of Eu(III) was studied in presence of 1.00 × 10 −3 M CO 3 2− ions under varying pH (7.0 to 9.0) using 8.80 × 10 −2 M SA at I = 0.20 M (NaClO 4 ). Fig.…”

“…The dissolution of the silica/aluminosilicate mineral present in the vicinity of the stored waste is expected to influence the chemistry and subsequent migration of actinides and fission products released from these high-level wastes. Recent studies on silica dissolution have indicated that the dissolved silica concentration may reach as high as 0.1 M and, therefore, can become a significant complexant of the released cations [3]. To further complicate this system, monomeric silicates can react to form polynuclear species leading to metastable equilibrium mixtures of colloidal particles plus monomeric dissolved silicate [4][5][6][7].…”