Formation of Apatite in Hanford Vadose Zone Sediments by Gaseous Injection of Phosphorus Compounds
EMSL Project ID
23593
Abstract
Large regions of strontium-90 and technetium-99 contamination exist in the unsaturated zone at Hanford at depths that are impractical for excavation. No active remediation options have been developed to date for these deep, unsaturated zone plumes, but they continue to pose a significant potential future risk to groundwater resources. We propose to evaluate the use of gas-phase injection of phosphorus compounds (e.g. triethyl phosphate, TEP) into unsaturated porous media to provide a source of phosphorus for apatite formation. Apatite is known to sequester 90Sr and recent evidence suggests that it may also sequester 99Tc under favorable geochemical conditions. Apatite has very low aqueous solubility (Ksp  10-44), so if apatite can be formed in unsaturated porous media by injection of a gaseous phosphorus source, it may provide a means of permanently immobilizing contaminants such as 90Sr and 99Tc and other heavy metals in deep unsaturated zones that are inaccessible by other means. Unlike aqueous injection of reactive chemicals, gaseous injection poses little to no risk for mobilizing contaminants in the unsaturated (a.k.a. vadose) zone.
Project Details
Project type
Exploratory Research
Start Date
2007-10-29
End Date
2008-11-02
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members