Spectroscopic and Microscopic Characterization of Contaminant Uptake and Retention by Carbonates in the Soil and Vadose Zone
EMSL Project ID
1639
Abstract
Contamination by toxic metals and radionuclides at numerous sites across the DOE Complex poses serious challenges for the design and implementation of effective remediation measures. The mobility of contaminants is a primary concern for the assessment and prediction of their distribution in the groundwater, soil, and vadose zones as well as for the development of technologies appropriate for their recovery or isolation. The chemical inventory of contaminants of major concern includes metals such as Cs, Co, Cr, Pb, Sr, and U. Uptake and retention of these metals by reaction with mineral phases in the subsurface environment are major processes that govern their mobility and fate over time scales relevant to site histories and the DOE mission. The reactive properties of metal contaminants are dependent on numerous factors including the fluid composition, the nature of mineral phases present (i.e., their identity, chemical composition, and availability of reactive sites on their surfaces), and the metal's chemical and physical state (including chemical identity, oxidation state, bound ligands, and molecular structure; collectively referred to as speciation). Carbonate minerals (particularly calcite) are important components in the soil and vadose zone of several DOE sites (e.g., Hanford Site). Because they can form rapidly and are highly reactive, carbonates may be extremely effective in attentuating transport of toxic metals and radionuclides by several uptake mechanisms, including co-precipitation and adsoprtion. In contrast to the sorptive behavior shown by many hydr/oxide and clay minerals, sorptive uptake of dissolved metals onto calcite usually results in co-precipitation. This has important implications for the long-term retention of contaminants, since metal species are incorporated into the bulk, rather than solely at the surface of the crystal, and bulk dissolution is necessary for their re-release to fluids.
Project Details
Project type
Exploratory Research
Start Date
1999-07-28
End Date
2002-09-09
Status
Closed
Released Data Link
Team
Principal Investigator