Thesis
Impact of leached ettringite stability and transformation on incorporated iodine retention
Washington State University
Master of Science (MS), Washington State University
05/2020
DOI:
https://doi.org/10.7273/000004056
Handle:
https://hdl.handle.net/2376/125033
Abstract
Ettringite [Ca6Al2(SO4)3(OH)12ยท26H2O] found in cementitious waste forms (CWFs) is known to immobilize iodate (IO3-) via sulfate (SO42-) substitution, yet poor iodine retention in CWFs for nuclear waste storage remains a challenge. In this study, ettringite mineral transformation and iodine release from IO3--incorporated ettringite ((IO3-)-Ett) was investigated to determine the mechanisms driving IO3- release in environmentally relevant solutions of varying composition, pH, and alkalinity. (IO3-)-Ett was leached in six simulated solutions relevant to the Hanford Site (Washington State, USA) for a period of 56 days: DDI, 24 ppm CO32-, 1400 ppm SO42-, Hanford groundwater, Hanford vadose zone porewater and a cement equilibrated solution. By monitoring IO3- uptake and removal and characterizing changes in the solid material, incongruent dissolution of ettringite to calcite and oxyanion substitution into the ettringite structure (e.g. SO42- or CO32-) were identified as IO3- release mechanisms. In general, higher concentrations of SO42- and CO32-, and lower alkalinity and pH, result in greater iodine release. However, the formation of secondary minerals, e.g., calcite, may re-incorporate IO3- (pH < 10). These results provide valuable insight into iodine release from CWFs that may be used to improve current CWF formulations for the treatment of iodine-containing nuclear waste.
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Details
- Title
- Impact of leached ettringite stability and transformation on incorporated iodine retention
- Creators
- Nancy Maria Avalos
- Contributors
- Allan Stan Felsot (Advisor) - Washington State University, Department of Entomology
- Awarding Institution
- Washington State University
- Academic Unit
- School of the Environment (CAS)
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University
- Identifiers
- 99900890792601842
- Language
- English
- Resource Type
- Thesis