Biogeochemical mineralogical, and hydrological characteristics of an iron reactive barrier used for treatment of uranium and other contaminants

Book · Wed May 01 00:00:00 EDT 2002

OSTI ID:986467

Gu, Baohua ^[1]; Watson, David B ^[1]; Phillips, Debra H ^[2]; Liang, Liyuan ^[1]

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1. ORNL
2. Queen's University, Belfast

A permeable iron reactive barrier was installed in late November, 1997 at the U.S. Department of Energy's Y-12 National Security Complex in Oak Ridge, Tennessee. The overall goal of this research was to determine the effectiveness of the use of zero-valent iron (Fe{sup 0}) to retain or remove uranium and other contaminants such as technetium and nitrate in groundwater. The long-term performance issues were investigated by studying the biogeochemical interactions between Fe{sup 0} and groundwater constituents and the mineralogical and biological characteristics over an extended field operation. Results from nearly 3 years of monitoring indicated that the Fe{sup 0} barrier was performing effectively in removing contaminant radionuclides such as uranium and technetium. In addition, a number of groundwater constituents such as bicarbonates, nitrate, and sulfate were found to react with the Fe{sup 0}. Both nitrate and sulfate were reduced within or in the influence zone of the Fe{sup 0} with a low redox potential (i.e., low Eh). An increased anaerobic microbial population was also observed within and in the vicinity of the Fe{sup 0} barrier, and these microorganisms were at least partially responsible for the reduction of nitrate and sulfate in groundwater. Decreased concentrations of Ca{sup 2+} and bicarbonate in groundwater occurred as a result of the formation of minerals such as aragonite (CaCO{sub 3}) and siderite (FeCO{sub 3}), which coincided with the Fe{sup 0} corrosion and an increased groundwater pH. A suite of mineral precipitates was identified in the Fe{sup 0} barrier system, including amorphous iron oxyhydroxides, goethite, ferrous carbonates and sulfides, aragonite, and green rusts. These minerals were found to be responsible for the cementation and possibly clogging of Fe{sup 0} filings observed in a number of core samples from the barrier. Significant increases in cementation of the Fe{sup 0} occurred between two coring events conducted at {approx}1 year apart and appeared to correspond to the changes in an apparent decrease in hydraulic gradient and connectivity. The present study concludes that, while Fe{sup 0} may be used as an effective reactive medium for the retention or degradation of many redox-sensitive contaminants, its long-term reactivity and performance could be severely hindered by its reactions with other groundwater constituents; and groundwater flow may be restricted because of the build up of mineral precipitates at the soil/Fe{sup 0} interface. Depending on the site biogeochemical conditions, the rate of Fe{sup 0} corrosion may increase; therefore, the life span of the Fe{sup 0} barrier could be shorter than predicted in previous studies ({approx}15-30 years).

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 986467
• Country of Publication: United States
• Language: English

Related Subjects

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
ACID CARBONATES
ARAGONITE
CARBONATES
CORROSION
GOETHITE
HYDRAULICS
IRON
LIFE SPAN
MICROORGANISMS
MONITORING
NATIONAL SECURITY
NITRATES
RADIOISOTOPES
REDOX POTENTIAL
RETENTION
SIDERITE
SULFATES
SULFIDES
TECHNETIUM
URANIUM