Neptunium(V) adsorption to bacteria at low and high ionic strength

Conference · Wed Dec 08 00:00:00 EST 2010

OSTI ID:1043469

Ams, David A ^[1]; Swanson, Juliet S ^[1]; Reed, Donald T ^[1]; Fein, Jeremy B ^[2]

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1. Los Alamos National Laboratory
2. UNIV OF NOTRE DAME

Np(V) is expected to be the predominant oxidation state of neptunium in aerobic natural waters. Np(V), as the NpO{sub 2}{sup +} aquo and associated complexed species, is readily soluble, weakly interacting with geologic media, and has a high redox stability under a relatively wide range of subsurface conditions. These chemical properties, along with a long half-life make it a primary element of concern regarding long-term nuclear waste storage and subsurface contaminant. The fate and transport of neptunium in the environment may be influenced by adsorption onto bacterial surfaces. The adsorption of neptunium to bacterial surfaces ties the mobility of the contaminant to the mobility of the bacterium. In this study, the adsorption of the neptunyl (NpO{sub 2}{sup +}) ion was evaluated at low ionic strength on a common soil bacterium and at high ionic strength on a halophilic bacterium isolated from a briny groundwater near the Waste Isolation Pilot Plant (WIPP) in southeast New Mexico. Adsorption experiments were performed in batch reactors as a function of pH, ionic strength, and bacterialNp mass ratio. Np(V) adsorption was modeled using a surface complexation approach with the mathematical program FITEQL to determine functional group specific binding constants. The data from acid and base titrations of the bacteria were also modeled to estimate the concentrations and deprotonation constants of discrete bacterial surface functional groups. Bacterial functional group characteristics and Np(V) adsorption behavior between the soil bacterium and the halophilic bacterium were compared. These results highlight the key similarities and differences in actinide adsorption behavior in environments of significantly different ionic strength. Similarities in adsorption behavior may be linked to similarities in the characteristics of the moieties between all bacterial cell walls. Differences in adsorption behavior may reflect differences in ionic strength effects, rather than differences in bacteria type, as the electronic double layer is compressed with increasing ionic strength. These results further highlight the importance of electrostatic interactions in the adsorption process between dissolved metals and bacterial surfaces. This work expands the understanding of actinide-bacteria adsorption phenomena to high ionic strength environmental conditions that are relevant as an aid to predicting Np(V) fate and transport behavior in areas such as the vicinity of salt-based nuclear waste repositories and high ionic-strength deep ground waters at DOE sites.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC52-06NA25396
• OSTI ID: 1043469
• Report Number(s): LA-UR-10-08178; LA-UR-10-8178; TRN: US1203236
• Resource Relation: Conference: American Geophysical Union Fall 2010 Meeting ; December 13, 2010 ; San Francisco, Ca
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
54 ENVIRONMENTAL SCIENCES
59 BASIC BIOLOGICAL SCIENCES
ACTINIDES
ADSORPTION
BACTERIA
CELL WALL
CHEMICAL PROPERTIES
CONTAMINATION
ENVIRONMENTAL TRANSPORT
GROUND WATER
MEETINGS
NEPTUNIUM
RADIOACTIVE WASTE STORAGE
SURFACES