Environmental Applications of Xanes: Speciation of Tc In Cement After Chemical Treatment and Se After Bacterial Uptake

Abstract

XANES (X-ray Absorption Near Edge Spectroscopy) has been employed to evaluate the efficacy of a process designed to encapsulate and reduce TcO4-in cement matrices, thereby immobilizing Tc. The oxidation state of Se following bioremediation of Se by bacteria has also been determined by XANES. The XANES measurements were performed at the Stanford Synchrotron Radiation Laboratory (SSRL) and the National Synchrotron Light Source (NSLS) at the respective K edges of Tc (21.0 keV) and Se (12.7 keV). Comparison of the XANES spectra of Tc in untreated cement to Tc in slag treated cement and to the chemical shifts of reference materials, shows that the oxidation state of Tc is the same in both cements. Thus, the addition of a reducing agent to the cement formulation does not significantly reduce the TcO4-. The common soil bacterium,Bacillus subtilis, is known to incorporate Se on or within the cell wall when exposed to a Se(IV) solution. The Se XANES spectra ofB. subtilis, as well as bacillus isolated from selenium rich soil, show that the organisms reduce selenite to the red allotrope of elemental Se.

Long-Term Technetium Interactions With Reducing Cementitious Materials

“…From a project conducted in the late 1990s, Lawrence Berkeley National Laboratory (LBNL) issued several reports and manuscripts on the subject of Tc interaction with saltstone (Shuh et al 1994;Shuh et al 2000;Allen et al 1997;Lukens et al 2005). These studies used X-ray absorption fine structure (XAFS) spectroscopy to determine the speciation of Tc in the solid phase.…”

Chemical Speciation Studies of Radionuclides by XAFS

“…Leaching of Tc from cement waste forms may be decreased by the used of additives such as blast furnace slag (BFS) which has been proposed to reduce the pertechnetate anion, TcO;, to a less soluble species such as Tc02 121. Herein, XAFS has been used to measure changes in Tc speciation induced by the addition of different chemical additives [3].…”

Investigation of different human pathogenic and food contaminating bacteria and moulds grown on selenite/selenate and tellurite/tellurate by X-ray absorption spectroscopy

“…Fricker, 1987). The mechanism of selenite toxicity is still unclear and the chemical selenium speciation after growth on selenite or selenate has not been determined in situ so far apart from two reports on Bacillus subtilis (Shuh et al, 1993) and Rhodobacter sphaeroides (Van Fleet-Stalder, Chasteen, Pickering, George, & Prince, 2000). Similar to the use of selenite containing selective media, the tellurite containing Baird-Parker agar is the standard agar for the isolation and identification of S. aureus from different foods.…”

“…Selenite and tellurite can be also found in the environment and can be reduced by microorganisms. For example, it is reported that Bacillus subtilis, an aerobic soil bacterium, is able to incorporate selenite and to reduce it to selenium ''somewhere within the vegetative bacterial cells'' (Shuh et al, 1993). The mechanism, however, is not understood.…”