Residual Waste from Hanford Tanks 241-C-203 and 241-C-204. 2. Contaminant Release Model
Fusion analyses, water leaches, selective extractions, empirical solubility measurements, and thermodynamic modeling were used with results from solid-phase characterization studies [see companion paper (1)] to determine total concentrations, contaminant-phase associations, and develop contaminant release models for residual sludge from single-shell underground waste tanks 241-C-203 and 241-C-204 at the U.S. Department of Energy?s Hanford Site in southeastern Washington state. U and Tc are primary contaminants of concern because of their long half-lives and their generally high mobility in oxidizing soil and groundwater environments. Uranium release was determined to be controlled by two phases; ?ejkaite [Na4(UO2)(CO3)3] and poorly crystalline Na2U2O7 [or clarkeite Na[(UO2)O(OH)](H2O)0-1] which were identified in C-203 and C-204 sludge samples (1). U release was determined to occur in three stages from these phases. In the first stage, U release will be controlled by the solubility of ?ejkaite, which is suppressed by high concentrations of sodium released from dissolution of NaNO3 in the residual sludges. Equilibrium solubility calculations indicate the U released during this stage will have a maximum concentration of 0.021 M. When all the NaNO3 has dissolved from the sludge, the solubility of the remaining ?ejkaite will increase to 0.28 M. After ?ejkaite has completely dissolved, the maximum concentration of U released is expected to be controlled by the solubility of Na2U2O7 at a concentration of 3.0 ? 10-5 M. For Tc, a significant fraction of its concentration in the residual sludge was determined to be relatively insoluble (20 wt% for C-203 and 80 wt% for C-204). Because of the low concentrations of Tc in these sludge materials, the characterization studies did not identify any discrete Tc solids phases. Therefore, release of the readily soluble fraction of Tc was assumed to be controlled by the solubility of NaTcO4 at 7.1 M. Selective extraction results indicated that the recalcitrant fraction of Tc was associated with Fe oxides. Release of the recalcitrant fraction of Tc was assumed to be controlled by dissolution of Fe oxide in the form of ferrihydrite. Based on this assumption and measured values for the ratio of recalcitrant Tc to total Fe in each bulk sludge, the release concentration of the recalcitrant fraction of Tc was calculated to be 3.9 ? 10-12 M for C-203 and 10.0 ? 10-12 M for C-204.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 884817
- Report Number(s):
- PNNL-SA-45611; ESTHAG; 830403000; TRN: US0603692
- Journal Information:
- Environmental Science and Technology, Vol. 40, Issue 12; ISSN 0013-936X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Inhibited Release of Mobile Contaminants from Hanford Tank Residual Waste
Hanford Tanks 241-C-203 and 241 C 204: Residual Waste Contaminant Release Model and Supporting Data