Technetium Attenuation in the Vadose Zone: Role of Mineral Interactions

Hess, Nancy J. ; Conradson, Steven D. ; McKinley, James P. ; Rai, Dhanpat ; Wildung, Raymond E. ; Krupka, Kenneth M.

Los Alamos National Laboratory

关键词: Attenuation;    Sediments;    37 Inorganic, Organic, Physical And Analytical Chemistry;    Clays;    Adsorption;   

DOI  :  10.2172/833639
RP-ID  :  EMSP-70177--2001
RP-ID  :  833639

美国|英语

来源: UNT Digital Library

【 摘 要 】

In the subsurface environment, the pertechnetate ion, Tc{sup VII}O{sub 4}{sup -}, forms only weak surface complexes with hydroxylated surface sites on clays and Al and Fe{sup III} oxides, and consequently, is weakly sorbed by most sediments and subsurface materials. Thus, adsorption of Tc{sup VII} onto these surfaces is not a viable mechanism for the attenuation of Tc in unsaturated subsurface environments or the vadose zone. Only the reduction of Tc{sup VII} to Tc{sup IV}, which results in the precipitation of low-solubility solids, will result in retention of Tc in the vadose zone. Possible reduction mechanisms are (1) homogeneous reduction, (2) microbial reduction, and (3) heterogeneous reduction on mineral surfaces. The redox conditions in the vadose zone in the western United States are likely too oxidizing for homogeneous reduction of Tc{sup VII} or to support a viable, widely distributed population of Fe-reducing organisms that can reduce Tc directly or indirectly. Thus, the purpose of this research is the investigation of heterogeneous reduction of Tc{sup VII} on Fe{sup II}-containing mineral surfaces and the stability of the resulting precipitated Tc solids.